Heavy weather
It has been a year of extremes in the northwest of England. Last November, Cumbria suffered some of the worst flooding in the UK’s recorded history. The River Derwent flooded Cockermouth, causing one death and £100million worth of damage. A single day saw 314 millimetres of rain fall, a 24-hour record for the UK, yet within seven months, the local water company had issued a drought order after the region’s driest start to the year in more than 70 years.
Such extreme and erratic weather – devastating floods, severe droughts, hurricanes, snowstorms and heat waves – is occurring around the world, and often with far greater intensity and loss of life than the Lake District experienced. Conventional wisdom suggests that something is up with the planet’s weather, and the perceptions of this change are striking in that they are geographically widespread.
The World Meteorological Organization (WMO) – drawing on climate data from networks of land-based weather and climate stations, ships and buoys from its 189 member states – reported that most parts of all continents experienced above-normal temperatures last year. Maximum daily temperatures in northern China were routinely above 40°C, breaking historical records; Australia had its third-warmest year on record, marked by three exceptional heat waves, one of which brought Victoria’s highest recorded temperature (48.8°C) and the worst bushfires in the country’s history.
Rainfall was also marked by extremes. China suffered its worst drought in five decades, with water levels in some reservoirs dropping to 50-year lows; India endured one of its weakest monsoons since 1972; drought in Kenya caused severe damage to livestock and a 40 per cent decline in the maize harvest; Mexico experienced severe-to-exceptional drought; and drought in central Argentina caused severe damage to agriculture, livestock and water resources.
Meanwhile, the northern plains of the USA were affected by record flooding, and the Amazon Basin had its second-worst floods in 100 years. Other areas experienced unprecedented bursts of intense rainfall: in Burkina Faso, 263 millimetres of rain, the highest in 90 years, was recorded in less than 12 hours; more than 300 millimetres was recorded in less than 48 hours in southeastern Spain, where the long-term annual average is 450 millimetres; and the highest September rainfall in 80 years produced severe flash floods in northwestern Turkey. Havoc also came in the form of extreme storms, with Ontario in particular experiencing record numbers of tornadoes and related fatalities.
Mounting evidence
Such weather extremes have always occurred, but scientists are now scrutinising and recording these events in search of evidence that they are increasing and that they are linked to climate change.
In 2007, the Intergovernmental Panel on Climate Change reported that there was ‘strong statistical evidence’ for a systemic change in extreme weather in some parts of the world, and the WMO is in no doubt. ‘There are data we’ve collected over the world for more than a century,’ says Omar Baddour, the WMO’s head of data management. ‘We can characterise an extreme event as one occurring less than ten per cent of the time when looking in the historical archives. We can say with confidence that extremes are becoming more frequent in many parts of the world.’
The consensus among forecasters is equally emphatic. In 2006, tropical cyclone researchers and forecasters gathered at a WMO meeting agreed that it was likely that some increase in tropical cyclone peak windspeed and rainfall will occur if the climate continues to warm. Model studies and theory, they announced, projected a three to five per cent increase in wind speed per degree Celsius increase of tropical sea-surface temperatures.
Simple science reinforces such a view, according to Bob Ward, policy director of the Grantham Research Institute on Climate Change and the Environment at the London School of Economics. ‘We know that the Earth is getting warmer, that can’t be disputed,’ he says. ‘On the purely theoretical basis of atmospheric physics, we expect to see a change in the frequency, intensity and distribution of extreme weather as a result of climate change. A warmer atmosphere contains more energy, and so you are more likely to have more extreme weather events. A warmer atmosphere holds more moisture, so we would expect to see changes in precipitation.’
Nevertheless, scientists are generally wary of committing to a direct link between severe weather and climate change, although many do believe the evidence firmly points that way. ‘You need a reasonable amount of data and it’s just not there yet,’ says Professor Meric Srokosz, co-ordinator of the rapid change programme at the National Oceanographic Centre, University of Southampton. ‘From a global perspective, the models show very clearly that we expect more droughts, rainfalls and storms. We are expecting more extreme events, but it’s unclear whether any such events have yet occurred.
‘I’m fairly comfortable with the thought that the climate models are predicting more extremes,’ he continues. ‘There are indications that something’s going on, but it’s difficult to say it’s definitely global warming.’
Experts from the Climatic Research Unit (CRU) at the University of East Anglia are equally cautious. ‘There is very likely a link between climate change and the characteristics of extreme weather events, but it isn’t a simple case of all types of extremes in all parts of the world increasing as the globe warms,’ says the CRU’s Dr Tim Osborn. ‘Our observations of what may already have happened, in terms of extreme events, are incomplete, and even where they are extensive, it isn’t an easy task to separate real trends from natural variability. It’s difficult to sign up 100 per cent to it.’
You might think that a hotter planet would explain the apparent increase in the prevalence of storms. The frequency of hurricanes in the North Atlantic has markedly increased since 1995, but, says Ward, ‘it’s still not clear if it is related to climate change or to oscillation’.
The UK’s Met Office admits that it, too, is uncertain. ‘The jury’s pretty much out as to whether climate change will lead to more storms,’ says Kirsty Lewis, principal climate change consultant for the Met Office’s Hadley Centre. ‘We really don’t know what’s going to happen. We’re more confident that storm surges will be more destructive in the future because they are related to sea-level rises, and we’re confident that sea levels will rise as a result of climate change.’
Recent hurricane statistics suggest that it pays not to draw too many conclusions from short-term figures. The 2009 Atlantic hurricane season was relatively placid and had the fewest named storms and hurricanes since 1997, although meteorologists ascribe this in part to unfavourable cyclonic conditions caused by an El Niño. In the western North Pacific, 22 named tropical storms were recorded, and 13 reached the intensity of typhoon, compared to the long-term average of 27, according to the WMO.
‘It’s much more difficult to attribute individual weather events to climate change,’ says Lewis. ‘It’s difficult to say whether we are seeing more extreme weather as a result of climate change or just because of variability in the climate. We tend to get a number of cycles – such as annual variability or decadal variability – and it’s sometimes difficult to say what is driving a particular variation in weather.
‘In terms of what we are observing now, it could, absolutely, be down to natural variability,’ she continues. ‘The forecast for the current hurricane season is around 20 named storms – that’s 12 more than the average in the region, but it’s well within the range of natural variability. The cold snap in the UK last winter was extreme, but again, it was within a range you could expect.’
Whether or not we will see more storms – or more intense storms – depends on a number of factors. ‘Weather is driven by energy from the sun heating the Earth’s surface and then that heat – in turn – warming the atmosphere,’ says Lewis. The equator gets more of this energy, and is warmer than the poles; and tropical cyclones are one of the mechanisms by which the Earth moves huge amounts of energy from the equator to the poles.
‘The way in which the Earth responds to more of the sun’s energy being trapped in the atmosphere is important in terms of how weather systems will be affected,’ she says. ‘Just because global average temperatures increase, that doesn’t necessarily mean more storms. The Earth’s atmosphere is complex and dynamic, and atmospheric turbulence is driven in part by imbalances of heat. Tropical cyclones are one manifestation of this turbulence, but modelling these features on climate change timescales is extremely difficult.’
Osborn agrees. ‘Windstorms and hurricanes are much more uncertain, both in terms of past trends and possible future changes,’ he says. ‘There is some indication that in some regions there may be fewer overall storms, but perhaps an increase in the most intense.’
This scenario has merit, suggests Srokosz. ‘People look at Hurricane Katrina – or the first recorded hurricane in the South Atlantic [in 2004] – this may be an indication of global warming, but while the statistics are suggestive of that, they aren’t conclusive. It’s an area of quite active research. It’s not necessarily that there will be more hurricanes – there might be the same number of hurricanes but they will be more intense.’
Climatologists in search of evidence of extreme weather events have focused on the 2003 European summer heat wave, which claimed 35,000 lives. Europe has yet to see a repeat of those extreme temperatures – average summer temperatures were 2°C higher than normal – but the Met Office has forecast that summers as hot as this could happen every other year by the 2040s. ‘We can expect more extreme high temperatures and heat waves – we can say that quite confidently,’ says Lewis. ‘The Mediterranean region and North Africa are getting a fairly consistent signal for a reduction in rainfall and higher temperatures.’
The alternative explanation for extreme events is that they are simply caused by natural variability, such as the Atlantic multi-decadal oscillation – a recognised natural phenomenon that makes waters warmer or cooler and seems to have an impact on the frequency of hurricanes. ‘The climate system is very complex, with many feedbacks between the ocean and the atmosphere,’ says Srokosz. ‘There’s a degree of random variation. The climate system doesn’t operate in a steady way. If there was no global warming, you would still get colder winters or hotter summers than usual.
‘Things are going on anyway and you are adding global warming on top. You have something kicking the weather system and you are kicking it again with global warming. It’s difficult to untangle which things are doing the kicking.’ Srokosz points to the North Atlantic Oscillation and the pressure differential between Iceland and the Azores. ‘It depends on the size of the pressure differential whether the storm tracks head towards the Mediterranean or to Norway and the UK. That’s nothing to do with global warming.’
Increasing severity
If the scientific community can’t make its mind up, others are more certain of a link between climate change and extreme weather. Insurers face paying out greater sums for damage caused by extreme weather – or indeed charging higher premiums or refusing to offer cover. According to a report by the insurers Swiss Re and the University of Bern, mid-latitude storms are increasing in severity and greater storm surges are likely to cause a significant long-term increase in coastal damage, and represent a major challenge in the future.
Studies of storm trends suggest that, by the end of this century, once-in-a-millennium storm-surge events could strike northern Europe every 30 years, with an increase in the height of peak storm surges of up to 55 per cent compared to today’s levels. ‘The sea wall that is rarely overtopped in the current climate will be overtopped much more frequently in the future,’ say the authors of the report, Natural Catastrophes and Man-made Disasters in 2009. ‘Extreme water levels seen once every 1,000 years could affect Denmark every five years, occur every 11 years in the UK, 13 years in Germany and every 15 years in the Netherlands.’
What about those who live in developing countries and are being exposed to greater extremes of weather? Aid organisations report that unusual and unseasonable events are occurring more frequently, including heavy rains in dry seasons, dry spells in rainy seasons, storms at unusual times, dense and lingering fogs, and huge temperature fluctuations.
‘A lot of our country programmes have developed an awareness of climate change through an observation of extreme events,’ says John Magrath, a climate change researcher at Oxfam. ‘They have to provide assistance in response to weather that is more extreme or unusual than they have experienced in the past.
‘There’s always a degree of subjectivity, but we are convinced that there are worrying trends of certain types of extreme weather,’ he continues. ‘That is against a backdrop where we are seeing less dramatic but worrying shifts in weather that increases people’s vulnerability should more violent events occur. As people face ever more erratic weather, the risks are increased.’
The most important impact is heavy rainfall, Magrath says, although he stresses that the weather doesn’t need to be exceptionally extreme to have a disastrous impact. ‘While we’re seeing more intense rain and storms, they are sub-hurricane, sub-cyclone in strength. Many of our country programmes have increasingly reported over the past 20 years that rainfall is more violent when it happens and that it comes in much more intense bursts. The rainy season also seems to be truncated, and the seasons have changed.’
In Vietnam, communities say that storms are increasingly tracking south into areas that had never experienced them and are more violent, bringing more floods; in Uganda, farmers report that the traditional long rains from March to June no longer fall consistently through the season, but rather in short, often localised torrents interspersed with hot, dry spells; in Malawi, farmers say that wind patterns have become ‘mixed up’ and are often stronger and more destructive. Nepal’s winter drought of 2008–09 was one of the worst in its history, and the country is experiencing more intense rainfall compressed into a smaller number of days, so it’s less useful.
‘Heavier rainfall triggers far more flooding, increases soil erosion, and damages crops and households,’ says Magrath. ‘Rainfall in shorter bursts means you have longer, hotter periods, so we’re seeing more droughts.’
These, in turn, have specific consequences. For example, during periods of low rainfall, women in rural communities are required to spend more time collecting water and firewood – according to Oxfam, a prolonged season of drought will see a woman spend seven hours collecting water, as opposed to one hour in normal conditions.
‘These are observed events,’ Magrath says. ‘We’re seeing these trends everywhere we work – from Malawi to Bolivia and Vietnam. Most people on the ground don’t tend to think about climate change – they just express bewilderment or fear about unprecedented events and how their world outlook is changing.’
Such trends have profound implications for what aid organisations call ‘disaster preparedness’, the ability of a community to fortify itself against extreme natural disasters. ‘You used to be able to plan for a flood or a drought,’ says Catherine Pettengell, Oxfam’s global adviser for climate change adaptation. ‘If you knew there was a one-in-100-year likelihood of a major flood, you could plan to improve people’s preparedness accordingly. We’ve always had historical yardsticks, but they aren’t enough any more. Those patterns are being disrupted.
‘If it was just a rare event or a one-off, communities could bounce back,’ she continues. ‘But if such events happen more frequently, you reduce the opportunity to bounce back. You can’t just eat less for a season, or adopt traditional coping strategies that poorer people have historically used. We’re seeing a rise in small- and medium-scale weather-related disasters, and that has a huge impact on how we are able to respond. You have to find a new way of making livelihoods sustainable.’
Oxfam’s attempts to mitigate more intense rainfall events have included collaboration with rural communities in Bolivia to construct a system of raised fields and seed beds. Gullies around fields help rainfall to run off without damaging the crops, while the raised beds retain more rain, which helps to offset the longer, drier periods between rainfall events. ‘We haven’t yet looked at how high these beds would need to be in the long term if the projections for more rainfall are correct,’ says Pettengell.
The countries currently most threatened by such trends are Honduras, Bangladesh and Myanmar, according to an annual global climate risk index compiled by Germanwatch, an organisation working to raise awareness of climate change. ‘We look at how much countries are affected by climate change and how much they are affected by extreme events – you can look at the impact of one on the other,’ says Sven Harmeling, senior adviser for climate change and development for Germanwatch. ‘Certain countries are much more vulnerable to extreme events.
And I think it’s very likely that we are seeing these events due to climate change.’
According to Germanwatch’s analysis, storms, floods and heat waves caused the deaths of 600,000 people and US$1.7trillion of losses and damage between 1990 and 2008. Honduras, Bangladesh and Myanmar suffered the highest combination of deaths and economic losses over the period. But while Myanmar and Honduras are rated highly because of single events (Cyclone Nargis in 2008 in Myanmar and Hurricane Mitch in Honduras in 1998), Bangladesh has been continuously hit by extreme weather.
‘Countries such as India and Bangladesh are frequently hit by extreme events, while Myanmar is less frequently affected but is still extremely vulnerable,’ says Harmeling.
‘A number of countries face more extreme events and have to prepare for this. They can argue for developed nations to cut their carbon emissions, but in reality, they need to be prepared and build early-warning systems.’
Disaster preparedness varies hugely from one country to another (see Planning for disasters), but several mitigation measures seem straightforward enough. ‘There’s a great role for government to reduce the magnitude of risk people are facing,’ says Magrath. ‘Social protection programmes – crop or weather insurance, cash or food for work and subsidies – can make a difference. We also have to manage resources more efficiently, and place more emphasis on helping existing crops cope with more rainfall and flooding.
‘Sometimes I think that when the chips are down, we are going to be innovative and solve some of the problems,’ he continues. ‘But some of the social measures don’t tend to need outside assistance – they only require changes in national policies and the allocation of fairly small sums in national budgets.’
Confirming the link
Proof of a clear, unarguable link between climate change and extreme weather remains elusive, but inaction, warns the WMO’s Baddour, could have grave consequences. ‘If the current trend in global warming continues, we have a likely scenario in which extreme weather events will become even more intense, more frequent and more devastating,’ he says. ‘We are talking in terms of a few decades ahead – 30–50 years or so. Extreme heat waves occurring once every 100 years now may occur every few years. What we now call extreme weather events will become common events in the future as a consequence of global warming.’
Politicians, however, tend only to react when the science is certain, a point Srokosz acknowledges readily – if wearily. ‘In another ten or 20 years, it should be clear, statistically, whether the models are correct or not,’ he says. ‘The temperature will have risen a bit more, extreme events will have increased. The trouble is that by the time we have that certainty, it may be too late to do much about it.’
El Niño/La Niña and global warming
The problem of linking extreme weather to climate change lies in the uncertainty over whether such events are actually being caused by recognised long-term weather patterns. The picture is complicated by the theory that climate change may, in turn, be influencing the behaviour of some of these natural climatic variations. Perhaps the best known are El Niño, where a feedback between the ocean and the atmosphere leads to a flip in the system, warm water moves from Indonesia to the east of the Pacific and global temperatures generally rise; and La Niña, where the eastern Pacific cools, with correspondingly cooler temperatures.
Every El Niño differs in magnitude and duration, according to the US National Oceanic and Atmospheric Administration (NOAA). ‘Warm El Niño episodes are characterised by an increased number of tropical storms and hurricanes in the eastern Pacific and a decrease in the Gulf of Mexico and the Caribbean Sea,’ according to officials at the NOAA’s Pacific Marine Environmental Laboratory (PMEL). It’s believed that El Niño conditions suppress the development of tropical storms and hurricanes in the Atlantic. Conversely, La Niña appears to stimulate hurricane formation.
The question of whether or not El Niño itself is now being disrupted by climate change – which would potentially lead to more extreme and erratic weather patterns around the world – seems to be keeping scientists awake long into the night. ‘It’s certainly plausible that global warming may affect El Niño, since both phenomena involve large changes in the Earth’s heat balance,’ according to the PMEL. ‘But no computer model yet can reliably simulate both El Niño and greenhouse gas warming together.
‘Depending on which model you choose to believe, you can get different answers. Some scientists have speculated that a warmer atmosphere is likely to produce stronger or more frequent El Niños, but some computer models indicate El Niños may actually be weaker in a warmer climate.’
‘One might expect a general change in climate to have an impact on existing natural cycles in the climate, but I’ve not yet seen any strong evidence for that,’ says the LSE’s Bob Ward. ‘A lot of natural climatic cycles aren’t themselves particularly well understood yet, nor how they might interact with climate change.’
Planning for disasters
It may come as a surprise, given its low level of income and poor infrastructure, but Cuba is often cited by aid organisations as the country best able to mitigate the impacts of extreme storms and flooding.
According to a report by Martha Thompson of Oxfam America, Cuba has displayed ‘exceptional dedication’ to preparing its population against disasters. The country has certainly had plenty of practice: its location in the mouth of the Gulf of Mexico puts it directly in the path of numerous hurricanes. Six major hurricanes hit Cuba between 1996 and 2002, yet only 16 people have died.
By comparison, Hurricane Isabel killed 22 people when it hit the mid-Atlantic USA in September 2003.
Cuba lays great emphasis on public education, meteorological research, early-warning systems and effective communication systems, such as tapping into the ham radio network. The civil defence structure requires widespread participation of the population in disaster preparedness, education in the use of local schools as evacuation shelters, and securing boats and buses for evacuation purposes. Plans are detailed to a level where ‘guardians’ in apartment blocks are responsible for assisting with the evacuation of single mothers and their children and wheelchair users.
A national planning authority designates the levels of risk for settlement of coastal areas, riversides and hillsides, which determine whether or not populations may occupy them, prioritising human safety over unbridled economic development. Chlorine tablets are even issued in advance to ensure potable water.
‘The government has worked hard to raise awareness,’ says Sven Harmeling of Germanwatch. ‘Children are instilled at an early age with how to react if a hurricane is coming. It’s possible to significantly reduce the number of people who die in such an event. The trouble is that most countries are restricted in what they can do because of limited resources.’
October 2010
Such extreme and erratic weather – devastating floods, severe droughts, hurricanes, snowstorms and heat waves – is occurring around the world, and often with far greater intensity and loss of life than the Lake District experienced. Conventional wisdom suggests that something is up with the planet’s weather, and the perceptions of this change are striking in that they are geographically widespread.
The World Meteorological Organization (WMO) – drawing on climate data from networks of land-based weather and climate stations, ships and buoys from its 189 member states – reported that most parts of all continents experienced above-normal temperatures last year. Maximum daily temperatures in northern China were routinely above 40°C, breaking historical records; Australia had its third-warmest year on record, marked by three exceptional heat waves, one of which brought Victoria’s highest recorded temperature (48.8°C) and the worst bushfires in the country’s history.
Rainfall was also marked by extremes. China suffered its worst drought in five decades, with water levels in some reservoirs dropping to 50-year lows; India endured one of its weakest monsoons since 1972; drought in Kenya caused severe damage to livestock and a 40 per cent decline in the maize harvest; Mexico experienced severe-to-exceptional drought; and drought in central Argentina caused severe damage to agriculture, livestock and water resources.
Meanwhile, the northern plains of the USA were affected by record flooding, and the Amazon Basin had its second-worst floods in 100 years. Other areas experienced unprecedented bursts of intense rainfall: in Burkina Faso, 263 millimetres of rain, the highest in 90 years, was recorded in less than 12 hours; more than 300 millimetres was recorded in less than 48 hours in southeastern Spain, where the long-term annual average is 450 millimetres; and the highest September rainfall in 80 years produced severe flash floods in northwestern Turkey. Havoc also came in the form of extreme storms, with Ontario in particular experiencing record numbers of tornadoes and related fatalities.
Mounting evidence
Such weather extremes have always occurred, but scientists are now scrutinising and recording these events in search of evidence that they are increasing and that they are linked to climate change.
In 2007, the Intergovernmental Panel on Climate Change reported that there was ‘strong statistical evidence’ for a systemic change in extreme weather in some parts of the world, and the WMO is in no doubt. ‘There are data we’ve collected over the world for more than a century,’ says Omar Baddour, the WMO’s head of data management. ‘We can characterise an extreme event as one occurring less than ten per cent of the time when looking in the historical archives. We can say with confidence that extremes are becoming more frequent in many parts of the world.’
The consensus among forecasters is equally emphatic. In 2006, tropical cyclone researchers and forecasters gathered at a WMO meeting agreed that it was likely that some increase in tropical cyclone peak windspeed and rainfall will occur if the climate continues to warm. Model studies and theory, they announced, projected a three to five per cent increase in wind speed per degree Celsius increase of tropical sea-surface temperatures.
Simple science reinforces such a view, according to Bob Ward, policy director of the Grantham Research Institute on Climate Change and the Environment at the London School of Economics. ‘We know that the Earth is getting warmer, that can’t be disputed,’ he says. ‘On the purely theoretical basis of atmospheric physics, we expect to see a change in the frequency, intensity and distribution of extreme weather as a result of climate change. A warmer atmosphere contains more energy, and so you are more likely to have more extreme weather events. A warmer atmosphere holds more moisture, so we would expect to see changes in precipitation.’
Nevertheless, scientists are generally wary of committing to a direct link between severe weather and climate change, although many do believe the evidence firmly points that way. ‘You need a reasonable amount of data and it’s just not there yet,’ says Professor Meric Srokosz, co-ordinator of the rapid change programme at the National Oceanographic Centre, University of Southampton. ‘From a global perspective, the models show very clearly that we expect more droughts, rainfalls and storms. We are expecting more extreme events, but it’s unclear whether any such events have yet occurred.
‘I’m fairly comfortable with the thought that the climate models are predicting more extremes,’ he continues. ‘There are indications that something’s going on, but it’s difficult to say it’s definitely global warming.’
Experts from the Climatic Research Unit (CRU) at the University of East Anglia are equally cautious. ‘There is very likely a link between climate change and the characteristics of extreme weather events, but it isn’t a simple case of all types of extremes in all parts of the world increasing as the globe warms,’ says the CRU’s Dr Tim Osborn. ‘Our observations of what may already have happened, in terms of extreme events, are incomplete, and even where they are extensive, it isn’t an easy task to separate real trends from natural variability. It’s difficult to sign up 100 per cent to it.’
You might think that a hotter planet would explain the apparent increase in the prevalence of storms. The frequency of hurricanes in the North Atlantic has markedly increased since 1995, but, says Ward, ‘it’s still not clear if it is related to climate change or to oscillation’.
The UK’s Met Office admits that it, too, is uncertain. ‘The jury’s pretty much out as to whether climate change will lead to more storms,’ says Kirsty Lewis, principal climate change consultant for the Met Office’s Hadley Centre. ‘We really don’t know what’s going to happen. We’re more confident that storm surges will be more destructive in the future because they are related to sea-level rises, and we’re confident that sea levels will rise as a result of climate change.’
Recent hurricane statistics suggest that it pays not to draw too many conclusions from short-term figures. The 2009 Atlantic hurricane season was relatively placid and had the fewest named storms and hurricanes since 1997, although meteorologists ascribe this in part to unfavourable cyclonic conditions caused by an El Niño. In the western North Pacific, 22 named tropical storms were recorded, and 13 reached the intensity of typhoon, compared to the long-term average of 27, according to the WMO.
‘It’s much more difficult to attribute individual weather events to climate change,’ says Lewis. ‘It’s difficult to say whether we are seeing more extreme weather as a result of climate change or just because of variability in the climate. We tend to get a number of cycles – such as annual variability or decadal variability – and it’s sometimes difficult to say what is driving a particular variation in weather.
‘In terms of what we are observing now, it could, absolutely, be down to natural variability,’ she continues. ‘The forecast for the current hurricane season is around 20 named storms – that’s 12 more than the average in the region, but it’s well within the range of natural variability. The cold snap in the UK last winter was extreme, but again, it was within a range you could expect.’
Whether or not we will see more storms – or more intense storms – depends on a number of factors. ‘Weather is driven by energy from the sun heating the Earth’s surface and then that heat – in turn – warming the atmosphere,’ says Lewis. The equator gets more of this energy, and is warmer than the poles; and tropical cyclones are one of the mechanisms by which the Earth moves huge amounts of energy from the equator to the poles.
‘The way in which the Earth responds to more of the sun’s energy being trapped in the atmosphere is important in terms of how weather systems will be affected,’ she says. ‘Just because global average temperatures increase, that doesn’t necessarily mean more storms. The Earth’s atmosphere is complex and dynamic, and atmospheric turbulence is driven in part by imbalances of heat. Tropical cyclones are one manifestation of this turbulence, but modelling these features on climate change timescales is extremely difficult.’
Osborn agrees. ‘Windstorms and hurricanes are much more uncertain, both in terms of past trends and possible future changes,’ he says. ‘There is some indication that in some regions there may be fewer overall storms, but perhaps an increase in the most intense.’
This scenario has merit, suggests Srokosz. ‘People look at Hurricane Katrina – or the first recorded hurricane in the South Atlantic [in 2004] – this may be an indication of global warming, but while the statistics are suggestive of that, they aren’t conclusive. It’s an area of quite active research. It’s not necessarily that there will be more hurricanes – there might be the same number of hurricanes but they will be more intense.’
Climatologists in search of evidence of extreme weather events have focused on the 2003 European summer heat wave, which claimed 35,000 lives. Europe has yet to see a repeat of those extreme temperatures – average summer temperatures were 2°C higher than normal – but the Met Office has forecast that summers as hot as this could happen every other year by the 2040s. ‘We can expect more extreme high temperatures and heat waves – we can say that quite confidently,’ says Lewis. ‘The Mediterranean region and North Africa are getting a fairly consistent signal for a reduction in rainfall and higher temperatures.’
The alternative explanation for extreme events is that they are simply caused by natural variability, such as the Atlantic multi-decadal oscillation – a recognised natural phenomenon that makes waters warmer or cooler and seems to have an impact on the frequency of hurricanes. ‘The climate system is very complex, with many feedbacks between the ocean and the atmosphere,’ says Srokosz. ‘There’s a degree of random variation. The climate system doesn’t operate in a steady way. If there was no global warming, you would still get colder winters or hotter summers than usual.
‘Things are going on anyway and you are adding global warming on top. You have something kicking the weather system and you are kicking it again with global warming. It’s difficult to untangle which things are doing the kicking.’ Srokosz points to the North Atlantic Oscillation and the pressure differential between Iceland and the Azores. ‘It depends on the size of the pressure differential whether the storm tracks head towards the Mediterranean or to Norway and the UK. That’s nothing to do with global warming.’
Increasing severity
If the scientific community can’t make its mind up, others are more certain of a link between climate change and extreme weather. Insurers face paying out greater sums for damage caused by extreme weather – or indeed charging higher premiums or refusing to offer cover. According to a report by the insurers Swiss Re and the University of Bern, mid-latitude storms are increasing in severity and greater storm surges are likely to cause a significant long-term increase in coastal damage, and represent a major challenge in the future.
Studies of storm trends suggest that, by the end of this century, once-in-a-millennium storm-surge events could strike northern Europe every 30 years, with an increase in the height of peak storm surges of up to 55 per cent compared to today’s levels. ‘The sea wall that is rarely overtopped in the current climate will be overtopped much more frequently in the future,’ say the authors of the report, Natural Catastrophes and Man-made Disasters in 2009. ‘Extreme water levels seen once every 1,000 years could affect Denmark every five years, occur every 11 years in the UK, 13 years in Germany and every 15 years in the Netherlands.’
What about those who live in developing countries and are being exposed to greater extremes of weather? Aid organisations report that unusual and unseasonable events are occurring more frequently, including heavy rains in dry seasons, dry spells in rainy seasons, storms at unusual times, dense and lingering fogs, and huge temperature fluctuations.
‘A lot of our country programmes have developed an awareness of climate change through an observation of extreme events,’ says John Magrath, a climate change researcher at Oxfam. ‘They have to provide assistance in response to weather that is more extreme or unusual than they have experienced in the past.
‘There’s always a degree of subjectivity, but we are convinced that there are worrying trends of certain types of extreme weather,’ he continues. ‘That is against a backdrop where we are seeing less dramatic but worrying shifts in weather that increases people’s vulnerability should more violent events occur. As people face ever more erratic weather, the risks are increased.’
The most important impact is heavy rainfall, Magrath says, although he stresses that the weather doesn’t need to be exceptionally extreme to have a disastrous impact. ‘While we’re seeing more intense rain and storms, they are sub-hurricane, sub-cyclone in strength. Many of our country programmes have increasingly reported over the past 20 years that rainfall is more violent when it happens and that it comes in much more intense bursts. The rainy season also seems to be truncated, and the seasons have changed.’
In Vietnam, communities say that storms are increasingly tracking south into areas that had never experienced them and are more violent, bringing more floods; in Uganda, farmers report that the traditional long rains from March to June no longer fall consistently through the season, but rather in short, often localised torrents interspersed with hot, dry spells; in Malawi, farmers say that wind patterns have become ‘mixed up’ and are often stronger and more destructive. Nepal’s winter drought of 2008–09 was one of the worst in its history, and the country is experiencing more intense rainfall compressed into a smaller number of days, so it’s less useful.
‘Heavier rainfall triggers far more flooding, increases soil erosion, and damages crops and households,’ says Magrath. ‘Rainfall in shorter bursts means you have longer, hotter periods, so we’re seeing more droughts.’
These, in turn, have specific consequences. For example, during periods of low rainfall, women in rural communities are required to spend more time collecting water and firewood – according to Oxfam, a prolonged season of drought will see a woman spend seven hours collecting water, as opposed to one hour in normal conditions.
‘These are observed events,’ Magrath says. ‘We’re seeing these trends everywhere we work – from Malawi to Bolivia and Vietnam. Most people on the ground don’t tend to think about climate change – they just express bewilderment or fear about unprecedented events and how their world outlook is changing.’
Such trends have profound implications for what aid organisations call ‘disaster preparedness’, the ability of a community to fortify itself against extreme natural disasters. ‘You used to be able to plan for a flood or a drought,’ says Catherine Pettengell, Oxfam’s global adviser for climate change adaptation. ‘If you knew there was a one-in-100-year likelihood of a major flood, you could plan to improve people’s preparedness accordingly. We’ve always had historical yardsticks, but they aren’t enough any more. Those patterns are being disrupted.
‘If it was just a rare event or a one-off, communities could bounce back,’ she continues. ‘But if such events happen more frequently, you reduce the opportunity to bounce back. You can’t just eat less for a season, or adopt traditional coping strategies that poorer people have historically used. We’re seeing a rise in small- and medium-scale weather-related disasters, and that has a huge impact on how we are able to respond. You have to find a new way of making livelihoods sustainable.’
Oxfam’s attempts to mitigate more intense rainfall events have included collaboration with rural communities in Bolivia to construct a system of raised fields and seed beds. Gullies around fields help rainfall to run off without damaging the crops, while the raised beds retain more rain, which helps to offset the longer, drier periods between rainfall events. ‘We haven’t yet looked at how high these beds would need to be in the long term if the projections for more rainfall are correct,’ says Pettengell.
The countries currently most threatened by such trends are Honduras, Bangladesh and Myanmar, according to an annual global climate risk index compiled by Germanwatch, an organisation working to raise awareness of climate change. ‘We look at how much countries are affected by climate change and how much they are affected by extreme events – you can look at the impact of one on the other,’ says Sven Harmeling, senior adviser for climate change and development for Germanwatch. ‘Certain countries are much more vulnerable to extreme events.
And I think it’s very likely that we are seeing these events due to climate change.’
According to Germanwatch’s analysis, storms, floods and heat waves caused the deaths of 600,000 people and US$1.7trillion of losses and damage between 1990 and 2008. Honduras, Bangladesh and Myanmar suffered the highest combination of deaths and economic losses over the period. But while Myanmar and Honduras are rated highly because of single events (Cyclone Nargis in 2008 in Myanmar and Hurricane Mitch in Honduras in 1998), Bangladesh has been continuously hit by extreme weather.
‘Countries such as India and Bangladesh are frequently hit by extreme events, while Myanmar is less frequently affected but is still extremely vulnerable,’ says Harmeling.
‘A number of countries face more extreme events and have to prepare for this. They can argue for developed nations to cut their carbon emissions, but in reality, they need to be prepared and build early-warning systems.’
Disaster preparedness varies hugely from one country to another (see Planning for disasters), but several mitigation measures seem straightforward enough. ‘There’s a great role for government to reduce the magnitude of risk people are facing,’ says Magrath. ‘Social protection programmes – crop or weather insurance, cash or food for work and subsidies – can make a difference. We also have to manage resources more efficiently, and place more emphasis on helping existing crops cope with more rainfall and flooding.
‘Sometimes I think that when the chips are down, we are going to be innovative and solve some of the problems,’ he continues. ‘But some of the social measures don’t tend to need outside assistance – they only require changes in national policies and the allocation of fairly small sums in national budgets.’
Confirming the link
Proof of a clear, unarguable link between climate change and extreme weather remains elusive, but inaction, warns the WMO’s Baddour, could have grave consequences. ‘If the current trend in global warming continues, we have a likely scenario in which extreme weather events will become even more intense, more frequent and more devastating,’ he says. ‘We are talking in terms of a few decades ahead – 30–50 years or so. Extreme heat waves occurring once every 100 years now may occur every few years. What we now call extreme weather events will become common events in the future as a consequence of global warming.’
Politicians, however, tend only to react when the science is certain, a point Srokosz acknowledges readily – if wearily. ‘In another ten or 20 years, it should be clear, statistically, whether the models are correct or not,’ he says. ‘The temperature will have risen a bit more, extreme events will have increased. The trouble is that by the time we have that certainty, it may be too late to do much about it.’
El Niño/La Niña and global warming
The problem of linking extreme weather to climate change lies in the uncertainty over whether such events are actually being caused by recognised long-term weather patterns. The picture is complicated by the theory that climate change may, in turn, be influencing the behaviour of some of these natural climatic variations. Perhaps the best known are El Niño, where a feedback between the ocean and the atmosphere leads to a flip in the system, warm water moves from Indonesia to the east of the Pacific and global temperatures generally rise; and La Niña, where the eastern Pacific cools, with correspondingly cooler temperatures.
Every El Niño differs in magnitude and duration, according to the US National Oceanic and Atmospheric Administration (NOAA). ‘Warm El Niño episodes are characterised by an increased number of tropical storms and hurricanes in the eastern Pacific and a decrease in the Gulf of Mexico and the Caribbean Sea,’ according to officials at the NOAA’s Pacific Marine Environmental Laboratory (PMEL). It’s believed that El Niño conditions suppress the development of tropical storms and hurricanes in the Atlantic. Conversely, La Niña appears to stimulate hurricane formation.
The question of whether or not El Niño itself is now being disrupted by climate change – which would potentially lead to more extreme and erratic weather patterns around the world – seems to be keeping scientists awake long into the night. ‘It’s certainly plausible that global warming may affect El Niño, since both phenomena involve large changes in the Earth’s heat balance,’ according to the PMEL. ‘But no computer model yet can reliably simulate both El Niño and greenhouse gas warming together.
‘Depending on which model you choose to believe, you can get different answers. Some scientists have speculated that a warmer atmosphere is likely to produce stronger or more frequent El Niños, but some computer models indicate El Niños may actually be weaker in a warmer climate.’
‘One might expect a general change in climate to have an impact on existing natural cycles in the climate, but I’ve not yet seen any strong evidence for that,’ says the LSE’s Bob Ward. ‘A lot of natural climatic cycles aren’t themselves particularly well understood yet, nor how they might interact with climate change.’
Planning for disasters
It may come as a surprise, given its low level of income and poor infrastructure, but Cuba is often cited by aid organisations as the country best able to mitigate the impacts of extreme storms and flooding.
According to a report by Martha Thompson of Oxfam America, Cuba has displayed ‘exceptional dedication’ to preparing its population against disasters. The country has certainly had plenty of practice: its location in the mouth of the Gulf of Mexico puts it directly in the path of numerous hurricanes. Six major hurricanes hit Cuba between 1996 and 2002, yet only 16 people have died.
By comparison, Hurricane Isabel killed 22 people when it hit the mid-Atlantic USA in September 2003.
Cuba lays great emphasis on public education, meteorological research, early-warning systems and effective communication systems, such as tapping into the ham radio network. The civil defence structure requires widespread participation of the population in disaster preparedness, education in the use of local schools as evacuation shelters, and securing boats and buses for evacuation purposes. Plans are detailed to a level where ‘guardians’ in apartment blocks are responsible for assisting with the evacuation of single mothers and their children and wheelchair users.
A national planning authority designates the levels of risk for settlement of coastal areas, riversides and hillsides, which determine whether or not populations may occupy them, prioritising human safety over unbridled economic development. Chlorine tablets are even issued in advance to ensure potable water.
‘The government has worked hard to raise awareness,’ says Sven Harmeling of Germanwatch. ‘Children are instilled at an early age with how to react if a hurricane is coming. It’s possible to significantly reduce the number of people who die in such an event. The trouble is that most countries are restricted in what they can do because of limited resources.’
October 2010
|
FIND OUT WHAT WE'RE TALKING ABOUT ON TWITTER:
| |
