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."