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Climate Reality check - a glance at the science behind Al Gore's project

  • 23 Sep 2011, 17:30
  • Tim Holmes

Al Gore's presentation for the Climate Reality Project was broadcast at midnight (GMT) last Thursday, and has garnered a certain amount of attention, particularly in North America.

A lot of the attention has focused on the social and political impacts of the campaign. But with presentations focusing on the "new normal" of increasing extreme weather events around the world, this post takes a look at some of the key claims on the different types of phenomena the Project's presenters focused on, and what links, if any, scientists have found between these and climate change.

Due to constraints of time and language, we looked at two presentations: Al Gore's from New York, and John Zavalney's from Boulder, Colorado. Our assessment is therefore not an in-depth look at the scientific worth of the Climate Reality project - that would take quite a lot longer - but an insight into the scientific merits of two sample presentations.

• "People are ... suffering the effects of the heatwaves" (Gore)

The European heatwave of 2003 was described by a 2008 US Climate Change Science Program report as "far outside the range of historical observations". A study of the heatwave concluded that:

"...It is very likely (confidence level >90%) that human influence has at least doubled the risk of a heatwave exceeding this threshold magnitude."

The US Climate Science report says of North America:

"Accompanying a general rise in the average temperature, most of North America is experiencing more unusually hot days and nights. The number of heat waves (extended periods of extremely hot weather) also has been increasing over the past fifty years... Human-induced warming has likely caused much of the average temperature increase in North America over the past fifty years and, consequently, changes in temperature extremes."

However, scientists studying the Russian heatwave of 2010 attributed it to natural climate variations, although they could not rule out climate change as a cause. Their work did indicate that the likelihood of extreme heatwaves in Russia will increase in the next few decades as greenhouse gases rise.

• "Longer and deeper droughts... killing crops and animals and people, driving up food prices and causing people to leave communities that they have called home for many generations..." (Gore)

A paper reviewing the link between drought and global warming ascribes drought to regions drying, the drying to temperature increases, and temperature increases in large part to human-generated greenhouse gases:

"Since the middle 20th century, global aridity and drought areas have increased substantially, mainly due to widespread drying... Since a large part of the recent warming is attributed to human-induced GHG [greenhouse gas] increases, it can be concluded that human activities have contributed significantly to the recent drying trend."

The World Food Programme state that:

"Drought is now the single most common cause of food shortages in the world. In 2006, recurrent drought caused crop failures and heavy livestock losses in parts of Ethiopia, Somalia and Kenya."

Stated estimates for deaths due to drought differ quite widely. UNESCO reports that droughts caused 280,000 deaths between 1991 and 2000, whilst the Centre for Research on the Epidemiology of Disasters suggests that droughts killed around 20,000 people per year between 1980 and 2008 - 558,000 in total. The UN Food and Agriculture Organisation puts the number of deaths substantially higher, estimating that droughts displaced 10 million farmers were displaced during the 1980s and that 1 million died.

"Droughts in Africa during the 1980s forced 10 million farmers to abandon their land; over 1 million died."

As Anna Mazhirov of the Columbia University Climate Center noted in March, there is a direct link between the increasing incidence of drought globally and rising food prices:

"Between 2006 and 2008, world average prices rose by 217 percent for rice, 136 percent for wheat, 125 percent for corn, and 107 percent for soybeans. Droughts in grain-producing regions were a leading cause for this world food price crisis, which led to food riots and political change."

• "fires ... spreading wildly and burning hotter and more intensely and burning longer ..." (Gore)
• "fires are ... spreading wildly, and burning hotter, longer and bigger" (Zavalney)

A 2004 Geophysical Research Letters paper found that:

"...Human-induced climate change has had a detectable influence on the area burned by forest fire in Canada over recent decades."

Whilst a 2006 Nature paper found that:

"...Increased wildfire activity over recent decades reflects sub-regional responses to changes in climate... the broad-scale increase in wildfire frequency across the western United States has been driven primarily by sensitivity of fire regimes to recent changes in climate over a relatively large area... the total area burned by these fires was more than six and a half times its previous level."

The EPA report "Climate Change Indicators in the United States" notes that:

"Some parts of the United States have experienced more warming than others ... The North, the West, and Alaska have seen temperatures increase the most".

As the US Climate Change Science Program concludes,

"although some part may have been played by decadal-scale variability... the trend is very likely attributable at least in part to long-term warming".

• "Bigger floods are ... wreaking havoc to more and more and more communities everywhere." (Zavalney)
• "bigger floods are ... wreaking havoc and destroying homes and businesses and killing people and destroying whole cultures" (Gore)

As a recent Nature paper found:

"...Human-induced increases in greenhouse gases have contributed to the observed intensification of heavy precipitation events found over approximately two-thirds of data-covered parts of Northern Hemisphere land areas."

This is supported by Kevin Trenberth's Climate Research paper which highlights a clear link between extremes in rainfall and rising temperatures, finding that "extreme flooding has increased in the 20th century". The study notes that estimates for world flood damage reach billions of US dollars, and that thousands of lives have been lost thanks to extreme rainfall events.

One problem in the Zalveney presentation, however, is the use of the word "everywhere", which - notwithstanding differences of potential interpretation - seems too strong. Trenberth's paper, for instance, notes only that "flooding has increased in some areas, and in association with tropical cyclones and hurricanes". Another is Gore's reference to "destroying whole cultures" - which is also surely too strong.

• "The big storms are becoming both more frequent and bigger." (Zavalney, slideshow)
• "Rainstorms are ... getting bigger and destroying communities and destroying lives" (Gore)
• "the storms are getting more intense" (Gore)
• "the winds and the storms are getting more and more and more destructive" (Zavalney)

Kevin Trenberth's paper (cited above) notes that:

"There is a direct influence of global warming on precipitation. ... [S]torms, whether individual thunderstorms, extratropical rain or snow storms, or tropical cyclones, supplied with increased moisture, produce more intense precipitation events. Such events are observed to be widely occurring".

In addition, "flooding has increased ... in association with tropical cyclones and hurricanes".

A 2008 Nature paper found that strong tropical storms are becoming stronger, concluding:

"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".

As Nature noted in an accompanying piece, this study found

"...A significant shift in distribution towards stronger storms that wreak the greatest havoc".

The US Climate Change Science Program's 2008 report on extreme weather and climate change notes that

"Atlantic tropical storm and hurricane destructive potential as measured by the Power Dissipation Index (which combines storm intensity, duration, and frequency) has increased... this increase is substantial since about 1970, and is likely substantial since the 1950s and 60s, in association with warming Atlantic sea surface temperatures... it is very likely that the human-induced increase in greenhouse gases has contributed to the increase in sea surface temperatures in the hurricane formation regions."

A recent Science paper finds that wind speeds increased globally between 1985 and 2008. However the study is unable to draw conclusions about links with climate change as the data used only covers two decades, not long enough to separate acceleration from multi-decadal natural variation.

Our ability to attribute observed trends has also been disputed in other papers. A 2010 Nature paper for instance, draws attention to the difficulties in making attributions:

"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."

A recent Climate Science Rapid Response Team briefing paper on severe thunderstorms and tornadoes is also circumspect. It concludes that while "[l]arge-scale climate change is also likely to affect small-scale phenomena like severe thunderstorms and tornadoes", the "nature and the degree of influence are very uncertain".

With regard to storms' "destructiveness", calculations of damages are also seen as inconclusive by some scientists. A 2011 Bulletin of the American Meteorological Society paper found that 22 studies demonstrated that weather-related natural hazards including storms and cyclones have increased economic losses around the world. However, this could not be attributed to manmade climate change.

Another paper states that:

"[r]ecent reviews have concluded that efforts to date have yet to detect or attribute an anthropogenic climate change influence on Atlantic tropical cyclone (of at least tropical storm strength) behaviour and concomitant damage."

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