This post is a compendium of recent scientist and science-informed views about the connection between man-made global warming and increased cyclone (hurricane) intensity.
As will become apparent from the quotations below, there have been different views at the cutting edge of research in this area of science (as is normal in science) but a recent international consensus has been established as set out in item #1 (Knutson et al, 2010): “Whether the characteristics of tropical cyclones have changed or will change in a warming climate — and if so, how — has been the subject of considerable investigation, often with conflicting results. Large amplitude fluctuations in the frequency and intensity of tropical cyclones greatly complicate both the detection of long-term trends and their attribution to rising levels of atmospheric greenhouse gases. Trend detection is further impeded by substantial limitations in the availability and quality of global historical records of tropical cyclones. Therefore, it remains uncertain whether past changes in tropical cyclone activity have exceeded the variability expected from natural causes. However, future projections based on theory and high-resolution dynamical models consistently indicate that greenhouse warming will cause the globally averaged intensity of tropical cyclones to shift towards stronger storms, with intensity increases of 2–11% by 2100. Existing modelling studies also consistently project decreases in the globally averaged frequency of tropical cyclones, by 6–34%. Balanced against this, higher resolution modelling studies typically project substantial increases in the frequency of the most intense cyclones, and increases of the order of 20% in the precipitation rate within 100 km of the storm centre. For all cyclone parameters, projected changes for individual basins show large variations between different modelling studies.”
1. Thomas R. Knutson, John L. McBride, Johnny Chan, Kerry Emanuel, Greg Holland, Chris Landsea, Isaac Held, James P. Kossin, A. K. Srivastava & Masato Sugi (from the Geophysical Fluid Dynamics Laboratory/NOAA, 201 Forrestal Road, Princeton, New Jersey 08542, USA; Centre for Australian Weather and Climate Research, Melbourne 3001, Australia; Guy Carpenter Asia-Pacific Climate Impact Centre, City University of Hong Kong, Kowloon, Hong Kong, China; Program in Atmospheres, Oceans, and Climate, Massachusetts Institute of Technology, Room 54-1620 MIT, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA; National Center for Atmospheric Research, Boulder, Colorado, USA; National Hurricane Center/NWS/NOAA, 11691 SW 17th Street, Miami, Florida 33165, USA; National Climatic Data Center/NOAA, 1225 W Dayton Street, Madison, Wisconsin 53706, USA; India Meteorological Department, Shivajinagar, Pune 411005, India; and Research Institute for Global Change, JAMSTEC, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, 236-0001 Kanagawa, Japan, respectively): “Whether the characteristics of tropical cyclones have changed or will change in a warming climate — and if so, how — has been the subject of considerable investigation, often with conflicting results. Large amplitude fluctuations in the frequency and intensity of tropical cyclones greatly complicate both the detection of long-term trends and their attribution to rising levels of atmospheric greenhouse gases. Trend detection is further impeded by substantial limitations in the availability and quality of global historical records of tropical cyclones. Therefore, it remains uncertain whether past changes in tropical cyclone activity have exceeded the variability expected from natural causes. However, future projections based on theory and high-resolution dynamical models consistently indicate that greenhouse warming will cause the globally averaged intensity of tropical cyclones to shift towards stronger storms, with intensity increases of 2–11% by 2100. Existing modelling studies also consistently project decreases in the globally averaged frequency of tropical cyclones, by 6–34%. Balanced against this, higher resolution modelling studies typically project substantial increases in the frequency of the most intense cyclones, and increases of the order of 20% in the precipitation rate within 100 km of the storm centre. For all cyclone parameters, projected changes for individual basins show large variations between different modelling studies.” .
2. Climate change, MSNBC, commenting on Knutson et al (2010) (item #1): “Top researchers now agree that the world is likely to get stronger but fewer hurricanes in the future because of global warming, seeming to settle a scientific debate on the subject. But they say there's not enough evidence yet to tell whether that effect has already begun. Since just before Hurricane Katrina hit Louisiana and Mississippi in 2005, dueling scientific papers have clashed about whether global warming is worsening hurricanes and will do so in the future. The new study seems to split the difference. A special World Meteorological Organization panel of 10 experts in both hurricanes and climate change — including leading scientists from both sides — came up with a consensus, which is published online Sunday in the journal Nature Geoscience… The study offers projections for tropical cyclones worldwide by the end of this century, and some experts said the bad news outweighs the good. Overall strength of storms as measured in wind speed would rise by 2 to 11 percent, but there would be between 6 and 34 percent fewer storms in number. Essentially, there would be fewer weak and moderate storms and more of the big damaging ones, which also are projected to be stronger due to warming… An 11 percent increase in wind speed translates to roughly a 60 percent increase in damage… The storms also would carry more rain, another indicator of damage… study suggests category 4 and 5 Atlantic hurricanes — those with winds more than 130 mph — would nearly double by the end of the century.” .
3. Greg Holland ( National Center for Atmospheric Research in Colorado) and Peter Webster (Georgia Institute of Technology)(2007): “We find that long-period variations in tropical cyclone and hurricane frequency over the past century in the North Atlantic Ocean have occurred as three relatively stable regimes separated by sharp transitions. Each regime has seen 50% more cyclones and hurricanes than the previous regime and is associated with a distinct range of sea surface temperatures (SSTs) in the eastern Atlantic Ocean. Overall, there appears to have been a substantial 100-year trend leading to related increases of over 0.7°C in SST and over 100% in tropical cyclone and hurricane numbers. It is concluded that the overall trend in SSTs, and tropical cyclone and hurricane numbers is substantially influenced by greenhouse warming. Superimposed on the evolving tropical cyclone and hurricane climatology is a completely independent oscillation manifested in the proportions of tropical cyclones that become major and minor hurricanes. This characteristic has no distinguishable net trend and appears to be associated with concomitant variations in the proportion of equatorial and higher latitude hurricane developments, perhaps arising from internal oscillations of the climate system. The period of enhanced major hurricane activity during 1945–1964 is consistent with a peak period in major hurricane proportions.” .
4. US Today, commenting on Holland and Webster (2007) (item #3) [with a graph of number of North Atlantic hurricanes per year versus time from 1850 to 2007]): “The number of hurricanes that develop each year has more than doubled over the past century, an increase tied to global warming, according to a study released Sunday."We're seeing a quite substantial increase in hurricanes over the last century, very closely related to increases in sea-surface temperatures in the tropical Atlantic Ocean," says study author Greg Holland of the National Center for Atmospheric Research in Colorado. Working with hurricane researcher Peter Webster of Georgia Institute of Technology, Holland looked at sea records from 1855 to 2005 in a study published in the British journal Philosophical Transactions of the Royal Society A. The researchers found that average hurricane numbers jumped sharply during the 20th century, from 3.5 per year in the first 30 years to 8.4 in the earliest years of the 21st century. Over that time, Atlantic Ocean surface temperatures increased .65 degrees, which experts call a significant increase… The new study drew criticism from experts who dispute the merits of combining data from the late 19th and early 20th centuries, when hurricane-tracking satellites didn't exist, with statistics gleaned from more modern technology.” .
5. Dr Andrew Ash (director, CSIRO’s Climate Adaptation Flagship) re climate change, floods and cyclones (2011): “We have had stronger cyclones in history and we have had cyclones just as large in size, but it is rare to get both a very large and intense cyclone. The flooding we have experienced to date on the whole has been within the bounds of historical events though in some areas, such as the Western Downs in Queensland and parts of Victoria, all time records have been broken. While extreme events like flooding and cyclones are an expected feature of La Nina events, the oceans around eastern and northern Australia are particularly warm at present. It is usual for the ocean in the Western Pacific to be warm during a La Nina event but the ocean temperatures are currently the highest on record…[In December 2010 the Southern Oscillation Index, a measure of the extent of La Nina, recorded a level of 27.1... the highest recorded December value in history] … The record warm temperatures are most likely a combination of La Nina and additional warming from human activities. While the flooding events and cyclones experienced this year aren't caused by climate change, the record warm ocean temperatures provide conditions more conducive to exacerbating these naturally occurring events associated with La Nina." .
6. Professor Tim Flannery (mammalogist, palaeontologist, environmentalist and 2007 Australian of the Year) re climate change, floods and cyclones (2011): “The individual severe weather events you point to are the kind of thing climate modelling predicts will become more frequent as greenhouse gas concentrations increase.” .
7. Australian Bureau of Meteorology (2006) re Tropical cyclones and climate change: “Leading scientists provide an expert view of the current state of knowledge. They note that there has been a high level of interest in the topic and that substantial debate is still occurring within the scientific community. With regard to the recent tropical cyclone seasons they conclude: "No single high impact tropical cyclone event of 2004 and 2005 can be directly attributed to global warming, though there may be an impact on the group as a whole.” Dr Geoff Love, the Australian Director of Meteorology, has submitted to the World Meteorological Organization's Commission for Atmospheric Sciences, meeting in Cape Town, South Africa, a "Statement on Tropical Cyclones and Climate Change". The Statement was prepared by an expert group of scientists comprising Dr John McBride and Dr Jeff Kepert of the Bureau of Meteorology in Australia, Professor Johnny Chan of China, Julian Heming of the UK, and Dr Greg Holland, Professor Kerry Emanuel, Thomas Knutson, Dr Hugh Willoughby and Dr Chris Landsea of the US. The paper reaffirms the finding of a 1998 study saying that any change in the frequency of tropical cyclones (hurricanes/typhoons) due to climate change cannot be determined due to a lack of knowledge and limitations of the available observing technologies. The little evidence that does exist indicates little or no change in global frequency. It also says that while some recent studies have suggested the intensity of tropical cyclones (hurricanes/typhoons) has increased substantially over the past 50 years due to climate change, the scientific community is "deeply divided". Some researchers believe the climate record is too inconsistent to draw such a conclusion due to changes in observations equipment and methods over time. The panel says it cannot come to a definitive conclusion in this "hotly debated area"… No single disaster caused by a tropical cyclone (hurricane/typhoon) in 2004 or 2005 - including Hurricane Katrina in the US - can be directly attributed to global warming. Rather, climate change may have an impact on the group as a whole. Further research is needed.” [6, 7].
8. Dr John McBride and Dr Jeff Kepert ( Bureau of Meteorology in Australia), Professor Johnny Chan (China), Julian Heming (UK), and Dr Greg Holland, Professor Kerry Emanuel, Thomas Knutson, Dr Hugh Willoughby and Dr Chris Landsea (US), “Statement on Tropical Cyclones and Climate Change" (2006): “No single high impact tropical cyclone event of 2004 and 2005 can be directly attributed to global warming, though there may be an impact on the group as a whole; Emanuel (2005) has produced evidence for a substantial increase in the power of tropical cyclones (denoted by the integral of the cube of the maximum winds over time) over the last 50 years. This result is supported by the findings of Webster et al (2005) that there has been a substantial global increase (nearly 100%) in the proportion of the most severe tropical cyclones (category 4 and 5 on the Saffir-Simpson scale), from the period from 1970 to 10995, which has been accompanied by a similar decrease in weaker systems. The research community is deeply divided over whether the results of these studies are due, at least in part, to problems in the tropical cyclone data base. Precisely, the historical record of tropical cyclone tracks and intensities is a product of real-time operations. Thus its accuracy and completeness changes continuously through the record as a result of the continuous changes and improvements in data density and quality, changes in satellite remote sensing retrieval and dissemination, and changes in training. In particular a step-function change in methodologies for determination of satellite intensity occurred with introduction of geosynchronous satellites in the mid to late 1970s. The division of the community on the Webster et al and Emanuel papers is not as to whether Global warming can cause a trend in tropical cyclone intensities. Rather it is on whether such a signal can be can be detected in the historical data base.” [6, 7, 8].
9. Quirin Schiermeier (writer for Nature, cartographer, graduate in geography, statistics and economics from the University of Munich) on global warming and hurricane intensity (2008): “As this year's Atlantic hurricane season becomes ever more violent, scientists have come up with the firmest evidence so far that global warming will significantly increase the intensity of the most extreme storms worldwide. The maximum wind speeds of the strongest tropical cyclones have increased significantly since 1981, according to research published in Nature this week [see #]. And the upward trend, thought to be driven by rising ocean temperatures, is unlikely to stop at any time soon… One of the most contentious issues in the climate-change debate has been whether the strength, number and duration of tropical cyclones will increase in a warmer world. Basic physics and modelling studies do suggest that tropical storms will become more intense, because warmer oceans provide more energy that can be converted into cyclone wind. But others believe that atmospheric changes might have an inhibiting role. Increasing shearing winds - another predicted consequence of global warming - are thought to suppress the cyclonic rotation of the storms, for example… The team statistically analysed satellite-derived data of cyclone wind speeds. Although there was hardly any increase in the average number or intensity of all storms, the team found a significant shift in distribution towards stronger storms that wreak the greatest havoc. This meant that, overall, there were more storms with a maximum wind speed exceeding 210 kilometres per hour (category 4 and 5 storms on the Saffir–Simpson scale). Rising ocean temperatures are thought to be the main cause of the observed shift. The team calculates that a 1 ºC increase in sea-surface temperatures would result in a 31% increase in the global frequency of category 4 and 5 storms per year: from 13 of those storms to 17. Since 1970, the tropical oceans have warmed on average by around 0.5 ºC. Computer models suggest they may warm by a further 2 ºC by 2100.” .
10. Elsner, J., Kossin, J. P. & Jagger, T. H. on global warming and increased tropical cyclone intensity (2008): “Atlantic tropical cyclones are getting stronger on average, with a 30-year trend that has been related to an increase in ocean temperatures over the Atlantic Ocean and elsewhere. Over the rest of the tropics, however, possible trends in tropical cyclone intensity are less obvious, owing to the unreliability and incompleteness of the observational record and to a restricted focus, in previous trend analyses, on changes in average intensity. Here we overcome these two limitations by examining trends in the upper quantiles of per-cyclone maximum wind speeds (that is, the maximum intensities that cyclones achieve during their lifetimes), estimated from homogeneous data derived from an archive of satellite records. We find significant upward trends for wind speed quantiles above the 70th percentile, with trends as high as 0.3±0.09ms-1yr-1 (s.e.) for the strongest cyclones. We note separate upward trends in the estimated lifetime-maximum wind speeds of the very strongest tropical cyclones (99th percentile) over each ocean basin, with the largest increase at this quantile occurring over the North Atlantic, although not all basins show statistically significant increases. Our results are qualitatively consistent with the hypothesis that as the seas warm, the ocean has more energy to convert to tropical cyclone wind.” .
11. Mark A. Saunders and Adam S. Lea (Benfield UCL Hazard Research Centre, Department of Space and Climate Physics, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT, UK) on sea surface warming and increased Atlantic hurricane activity (2009): “Atlantic hurricane activity has increased significantly since 1995, but the underlying causes of this increase remain uncertain. It is widely thought that rising Atlantic sea surface temperatures have had a role in this16, 17, but the magnitude of this contribution is not known. Here we quantify this contribution for storms that formed in the tropical North Atlantic, Caribbean Sea and Gulf of Mexico; these regions together account for most of the hurricanes that make landfall in the United States. We show that a statistical model based on two environmental variables—local sea surface temperature and an atmospheric wind field—can replicate a large proportion of the variance in tropical Atlantic hurricane frequency and activity between 1965 and 2005. We then remove the influence of the atmospheric wind field to assess the contribution of sea surface temperature. Our results indicate that the sensitivity of tropical Atlantic hurricane activity to August–September sea surface temperature over the period we consider is such that a 0.5°C increase in sea surface temperature is associated with a ~40% increase in hurricane frequency and activity. The results also indicate that local sea surface warming was responsible for ~40% of the increase in hurricane activity relative to the 1950–2000 average between 1996 and 2005. Our analysis does not identify whether warming induced by greenhouse gases contributed to the increase in hurricane activity, but the ability of climate models to reproduce the observed relationship between hurricanes and sea surface temperature will serve as a useful means of assessing whether they are likely to provide reliable projections of future changes in Atlantic hurricane activity.” .
12. Webster, P. J., Holland, G. J., Curry, J. A. & Chang, H.-R. on changes in tropical cyclone number, duration, and intensity in a warming environment (2005): “We examined the number of tropical cyclones and cyclone days as well as tropical cyclone intensity over the past 35 years, in an environment of increasing sea surface temperature. A large increase was seen in the number and proportion of hurricanes reaching categories 4 and 5. The largest increase occurred in the North Pacific, Indian, and Southwest Pacific Oceans, and the smallest percentage increase occurred in the North Atlantic Ocean. These increases have taken place while the number of cyclones and cyclone days has decreased in all basins except the North Atlantic during the past decade… We conclude that global data indicate a 30-year trend toward more frequent and intense hurricanes, corroborated by the results of the recent regional assessment. This trend is not inconsistent with recent climate model simulations that a doubling of CO2 may increase the frequency of the most intense cyclones, although attribution of the 30-year trends to global warming would require a longer global data record and, especially, a deeper understanding of the role of hurricanes in the general circulation of the atmosphere and ocean, even in the present climate state.” .
13. Professor Kerry Emanuel (Program in Atmospheres, Oceans, and Climate, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA) on warming and increased cyclone intensity (2005): “Theory and modelling predict that hurricane intensity should increase with increasing global mean temperatures, but work on the detection of trends in hurricane activity has focused mostly on their frequency and shows no trend. Here I define an index of the potential destructiveness of hurricanes based on the total dissipation of power, integrated over the lifetime of the cyclone, and show that this index has increased markedly since the mid-1970s. This trend is due to both longer storm lifetimes and greater storm intensities. I find that the record of net hurricane power dissipation is highly correlated with tropical sea surface temperature, reflecting well-documented climate signals, including multi-decadal oscillations in the North Atlantic and North Pacific, and global warming. My results suggest that future warming may lead to an upward trend in tropical cyclone destructive potential, and—taking into account an increasing coastal population—a substantial increase in hurricane-related losses in the twenty-first century.” .
14. Professor Kerry Emanuel, Ragoth Sundararajan, and John Williams (Program in Atmospheres, Oceans, and Climate, Massachusetts Institute of Technology, Cambridge, Massachusetts} on modeling showing cyclone storm intensity generally increases with global warming (2008): “Changes in tropical cyclone activity are among the more potentially consequential results of global climate change, and it is therefore of considerable interest to understand how anthropogenic climate change may affect such storms. Global climate models are currently used to estimate future climate change, but the current generation of models lacks the horizontal resolution necessary to resolve the intense inner core of tropical cyclones. Here we review a new technique for inferring tropical cyclone climatology from the output of global models, extend it to predict genesis climatologies (rather than relying on historical climatology), and apply it to current and future climate states simulated by a suite of global models developed in support of the most recent Intergovernmental Panel on Climate Change report. This new technique attacks the horizontal resolution problem by using a specialized, coupled ocean–atmosphere hurricane model phrased in angular momentum coordinates, which provide a high resolution of the core at low cost. This model is run along each of 2,000 storm tracks generated using an advection-and-beta model, which is, in turn, driven by large-scale winds derived from the global models. In an extension to this method, tracks are initiated by randomly seeding large areas of the tropics with weak vortices and then allowing the intensity model to determine their survival, based on large-scale environmental conditions. We show that this method is largely successful in reproducing the observed seasonal cycle and interannual variability of tropical cyclones in the present climate, and that it is more modestly successful in simulating their spatial distribution. When applied to simulations of global climate with double the present concentration of carbon dioxide, this method predicts substantial changes and geographic shifts in tropical cyclone activity, but with much variation among the global climate models used. Basinwide power dissipation and storm intensity generally increase with global warming, but the results vary from model to model and from basin to basin. Storm frequency decreases in the Southern Hemisphere and north Indian Ocean, increases in the western North Pacific, and is indeterminate elsewhere. We demonstrate that in these simulations, the change in tropical cyclone activity is greatly influenced by the increasing difference between the moist entropy of the boundary layer and that of the middle troposphere as the climate warms.” .
15. Professor Ross Garnaut (climate change economist and Australian Federal Government climate change adviser) warning that floods and cyclones like those experienced by Australian in 2011 will get more extreme as global warming increases (2011): “[while climate change cannot be directly blamed for the recent flooding, or for Cyclone Yasi] the greater energy in the atmosphere and the seas can intensify extreme events and I'm afraid that we're feeling some of that today, and we're feeling that at a time when global warming is in its early stages… [re carbon tax and climate change action] "Getting back in the saddle, I would like a result this time… We've taught ourselves that we're capable of making quite a big mess of dealing with this diabolical policy problem, I hope we've learnt something along the way…We haven't played our proportionate part amongst developed countries so far. We've talked about it from time to time, but we haven't done much…It will be quite important for the international effort that Australia ceases to be a drag on the international effort…I'm not talking about us leading the world, I'm talking about our catching up." .
16. Parliament of Australia, Parliamentary Library (that provides carefully researched infomation to members of the Australian Federal Parliament) : “Are extreme weather events—severe storms, flooding, droughts, heat waves or extremely violent cyclones—becoming more common? The answer appears to be 'yes'. Trends towards more powerful storms and hotter, longer dry periods have been observed, according to the IPCC's Fourth Assessment Report, and this trend is projected to continue.” .
17. Professor John Holdren (Professor of Environmental Policy at the Kennedy School of Government at Harvard University; Director of the Woods Hole Research Center; recent Chairman of the American Association for the Advancement of Science and President Obama’s chief scientific adviser) on climatic disruption (2008): “Harm is already occurring (continued). (Figure) Total power released by tropical cyclones (green: Annual mean HADISST 30S-30N) has increased (circa 2-fold 1990-2003) along with sea surface temperatures (blue: West Pac + East Pac + Atlantic); Kerry Emanuel, MIT, 2006”. .
18. Professor Vicky Pope (head of climate change advice at the Met Office, UK) explains how a warmer world is a wetter world (2011): "As the average global temperature increases one would expect the moisture content of the atmosphere to rise, due to more evaporation from the sea surface. For every 1C sea surface temperature rise, atmospheric moisture over the oceans increases by 6-8%. Also in general, as more energy and moisture is put into the atmosphere [by warming], the likelihood of storms, hurricanes and tornadoes increases." .
19. Dr Andrew Glikson (former Principal Research Scientist, Australian Geological Survey Organization, Earth and paleoclimate scientist. School of Archaeology and Anthropology, Research School of Earth Science, Planetary Science Institute, Australian National University) on Queensland floods [noting according to the report, that climate scientists were careful never to point to a single event as evidence of climate change but to examine medium and long-term trends] : “'Cyclones have increased twofold over the past 20 years. Floods have increased threefold. It's happening now, and it's happening faster than some of the climate-change scientists have dared to predict” .
20. William Cosgrove (vice president, World Water Council), 3rd World Water Forum, 2003: "Extreme weather records are [already] being broken every year and the resulting hydro-meteorological disasters claim thousands of lives and disrupt national economies," said of the Marseille-based think tank made up of users and suppliers of water for social and economic development. The big problem is that most countries aren't ready to deal adequately with the severe natural disasters that we get now, a situation that will become much worse as storms and droughts become more pervasive. Ignoring the problem is no longer an option… The increasing incidence of extreme events provides a convincing argument to continue looking into building partnerships between science, water managers and the disaster preparedness communities, including the development and dissemination of capacity development packages and methodologies. It is telling that disaster reduction has been recognized since 2000 an issue central to poverty reduction. ” [20, 21].
21. World Water Council press release from the 3rd World Water Forum re climate change, droughts and floods (February 2003): “Economic loses from weather and flood catastrophes have increased ten-fold over the past 50 years, partially the result of rapid climate changes, the World Water Council (WWC) says. These rapid climate changes are seen in more intense rainy seasons, longer dry seasons, stronger storms, shifts in rainfall and rising sea levels,. More disastrous floods and droughts have been the most visible manifestations of these changes. From 1971 to 1995, floods affected more than 1.5 billion people worldwide, or 100 million people per year, according to experts. This total includes 318,000 killed, and more than 81 million left homeless. Major floods that left at least 1,000 people dead and caused $1 billion in damages per episode have been the most destructive… According to climate experts, the expected climatic change during the 21st century will further intensify the hydrological cycle – with rainy seasons becoming shorter and more intense in some regions, while droughts in other areas will grow longer in duration, which could endanger species and crops and lead to drops in food production globally. Evidence for the link between climate change and increasing climate variability is mounting rapidly. For example, scientific research has linked the recent droughts in the USA and Afghanistan to the effects of global warming… These climate disasters stemming from climate variability include: Floods [and Droughts] - Based on data for ther period 1950 to 1998, the number of major flood disasters has grown considerably world-wide from decade to decade – six cases in the 1950s, seven in the 1960s, eight in the 1970s, 18 in the 1980s, and 26 in the 1990s. The number of significant flood disasters in the 1990s was higher than in the three previous decades combined. Overall, global precipitation is estimated to have increased by about two percent since 1900, though not on a uniform basis. This disparity in new rainfall caused some places to become wetter and others to get drier, such as North Africa south of the Sahara. In the most calamitous storm surge, the flood in Bangladesh in April 1991 killed 141,000 people. Two floods in China, one in 1996 and the second in 1998, caused the highest material losses of the decade, of the order of $30 billion and $26.5 billion, respectively. Floods also destroy the hard-won economic advances that many in the developing world have accomplished, such as the Mozambique floods of 2000, which left nearly 1 million homeless, and Hurricane Mitch in Central America . Comparing the economic impacts of the 2000 flood in Mozambique with the 2002 flood in Central Europe clearly illustrates the disparity in how national economies are impacted by extreme events. The cost of damages reflects the income levels of the countries. According to officials at the World Bank, the Mozambique flood resulted in a 45 percent drop in GDP in 2000, whereas in Germany, the 2002 flood is estimated to have caused less than a one percent drop in GDP…Hurricane Mitch  killed 11,000 people, with thousands of others missing. More than 3 million people were either homeless or severely affected. In this extremely poor regions, estimates of the total damage from the storm surpassed $5 billion. The President of Honduras, Carlos Flores Facusse, claimed the storm destroyed 50 years of progress. As far as the geographic distribution of the worst floods, the majority occurred in Asian countries … In addition, the impact of floods has had increasingly detrimental and disruptive effects on human health. In flooded areas, some diseases such as diarrhea, which kills 2.2 million children under th4 age of five per year, or leptospirosis (a systemic infection that can lead to meningitis and hemorrhagic jaundice) spread more rapidly… Many countries in Africa have been suffering from unprecedented droughts that may signal widespread climate change … Sea level rise is a concern in coastal and low-lying areas, including small islands. In addition to coastal flooding, saltwater intrusion into freshwater aquifers present a threat to water supplies. The average global sea level rise from 1900 to the year 2100 is expected to be 0.48 meters (19 inches), between twice and four times the rate of rise over the 20th century. The main effect on humans will be to confront extreme events such as storm surges. Areas of greatest danger include Small islands in the Pacific, mainly the Atolls; Coastal low-lying countries like Bangladesh and the Netherlands; Coastal mega-cities like Tokyo, Lagos, Buenos Aires and New York.” [20, 21].
22. Global Greenhouse Warming.com on climate and floods: "Meteorologic floods are by far the most common of the types of floods in the human experience, affecting parts of the globe every year. Such floods can bring good, such as the fertile soils formerly brought to the Nile Delta by annual flooding. However, large floods are mostly known for their catastrophic loss of life and property, such as in China and Bangladesh which repeatedly devastated by floods - Bangladesh lost 300,000 people in November 1970 and more than 130,000 in April 1991, from cyclone-induced flooding, and the massive flooding of the Yangtze River in China in 1931 caused more than 3 million deaths with a further 2 million in 1959 from flooding and starvation. …By 2025, half the world's population will be living in areas that are at risk from storms and other weather extremes," the World Water Council said, citing evidence gathered by U.N. and other experts. The economic cost of changes in climate and floods will be huge, especially for poor countries that are likely to bear the brunt of these events. The phrase Climate and Floods is something we will hear more of in the years ahead.”.
23. Dr James Hansen in “Storms of My Grandchildren” (2010): “Global warming does increase the intensity of droughts and heat waves, and thus the area of forest fires. However, because a warmer atmosphere holds more water vapour, global warming must also increase the intensity of the other extreme of the hydrological cycle – meaning heavier rains, more extreme floods, and more intense storms driven by latent heat, including thunderstorms, tornadoes, and tropical storms. I realized that I should have emphasized more strongly [in his 1988 testimony to a US Senate Committee] that both extremes increase with global warming.” .
24. American Association for the Advancement of Science (AAAS), 2006 (founded in 1848, AAAS serves some 262 affiliated societies and academies of science, serving 10 million individuals; the AAAS journal Science has the largest paid circulation of any peer-reviewed general science journal in the world, with an estimated total readership of 1 million): “The scientific evidence is clear: global climate change caused by human activities is occurring now, and it is a growing threat to society. Accumulating data from across the globe reveal a wide array of effects: rapidly melting glaciers, destabilization of major ice sheets, increases in extreme weather, rising sea level, shifts in species ranges, and more. The pace of change and the evidence of harm have increased markedly over the last five years. The time to control greenhouse gas emissions is now… In addition to rapidly reducing greenhouse gas emissions, it is essential that we develop strategies to adapt to ongoing changes and make communities more resilient to future changes. The growing torrent of information presents a clear message: we are already experiencing global climate change. It is time to muster the political will for concerted action. Stronger leadership at all levels is needed. The time is now. We must rise to the challenge. We owe this to future generations.” .
25. Senator Christine Milne (Australian Greens deputy leader; Tasmanian Greens senator) on man-made climate change and Cyclone Yasi (2011): “This is a tragedy, but it is a tragedy of climate change. The scientists have been saying that we are going to experience more extreme weather events, that their intensity is going to increase, their frequency.” 
. Thomas R. Knutson, John L. McBride, Johnny Chan, Kerry Emanuel, Greg Holland, Chris Landsea, Isaac Held, James P. Kossin, A. K. Srivastava & Masato Sugi, “Tropical cyclones and climate change”, Nature Geosciences, 3, 157 - 163 (2010): http://www.nature.com/ngeo/journal/v3/n3/abs/ngeo779.html .
. Climate change, MSNBC, “Study: stronger hurricanes loom. Fewer expected but bigger storms to bring more damage”, commenting on Knutson et al (2010), Climate change, MSNBC, 21 February 2010: http://www.msnbc.msn.com/id/35506750/ns/us_news-environment/ .
. Greg Holland and Peter Webster, “Heightened tropical cyclone activity in the North Atlantic: natural variability or climate trend?”, Philosophical Transactions of the Royal Society A, vol. 365, no. 1860. pp 2695-2716, 2007: http://rsta.royalsocietypublishing.org/content/365/1860/2695.short .
. US Today, “Study links more hurricanes, climate change”, 30 July 2007: http://www.usatoday.com/weather/hurricane/2007-07-29-more-hurricanes_N.htm .
. Matt Granfield, “Coincidence or climate change?’, ABC Drum Unleashed, 3 February 2011: http://www.abc.net.au/unleashed/43560.html .
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. Dr John McBride and Dr Jeff Kepert ( Bureau of Meteorology in Australia), Professor Johnny Chan (China), Julian Heming (UK), and Dr Greg Holland, Professor Kerry Emanuel, Thomas Knutson, Dr Hugh Willoughby and Dr Chris Landsea (US), “Statement on Tropical Cyclones and Climate Change", submitted to the World Meteorological Organization's Commission for Atmospheric Sciences, meeting in Cape Town, South Africa by Dr Geoff Love ( Australian Director of Meteorology), 2006: http://www.bom.gov.au/info/CAS-statement.pdf .
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