The report, published in the Bulletin of the American Meteorological Society,
investigates the causes of a wide variety of extreme weather and
climate events from around the world in 2013. Titled "Explaining Extreme
Events of 2013 from a Climate Perspective" the 84-page document
examines the causes of 16 individual extreme events - including heat waves, rain, flood, droughts and storms - that occurred on four continents in 2013.
Thirteen independent studies mentioned in the report - compiled by 92
scientists from around the globe – determined there was a link between
extreme weather and the burning of fossil fuels. But while the authors
found that human influence had substantially increased both the
likelihood and severity of heat waves in places like Asia and Australia,
it was more difficult to measure the influence of human activity on
other events like droughts, heavy rain and storms.
Thomas Peterson, principal scientist at NOAA's National Climactic Data
Center and one of the report's lead editors, says in an interview with Deutsche Welle TV Berlin, that
while scientists could not identify a linkage between human-caused
global warming and some extreme weather events, the data gathered
provides evidence that human activity has increased the intensity and
likelihood of heat waves in Asian countries such as China, Japan and
Korea.
Peterson: 'Human activity has influenced the strength of extreme weather or increased its likelihood'
Thomas Peterson: Each of the four topics evaluated in Asia was selected
by the author team for subjective reasons. Often because the event was
of interest to them on a personal level, as it impacted them, their
families and their friends. For instance, the report focuses on Japan,
Korea and China which all experienced extremely hot summers in 2013.
The fourth topic focused on heavy rain in India. With an early arrival
of monsoon-like atmospheric circulation in June, the heavy precipitation
that occurred in northern India was a once-in-a-century event.
The report found that long duration heat waves during the summer and
prevailing warmth for annual conditions are becoming increasingly likely
due to a warming planet, as much as 10 times more likely due to the
current cumulative effects of human-induced climate change, as found for
the Korean heat wave of summer 2013.
Extreme precipitation events of last year were found to have been much
less influenced by human-induced climate change than extreme temperature
events. Furthermore, prolonged cold waves have become much less likely,
such that the severely cold 2013 winter over the United Kingdom was
perhaps the most remarkable event of all those studied in 2013 - its
probability of occurrence may have fallen 30-fold due to global warming
alone.
However, there was no clear evidence of human influence on any of the
three very intense storms examined, which included a surprising
winter-like storm during autumn in the Pyrenees, an extreme blizzard
across the US High Plains, and Cyclone 'Christian' that delivered
damaging winds across northern Germany and southern Denmark.
All four events evaluated in Asia were found to indicate that human
activity had influenced the strength of extreme weather or increased its
likelihood. For instance, analyses of observed and simulated June
precipitation provided evidence that human-caused climate change has
increased the likelihood of much stronger precipitation in northern
India, and made heat waves more likely to occur in Japan, Korea and
Easter China.
Natural variability was a prime cause of all events, just the randomness
of the weather. For some of these events, in addition to the natural
causes, human influence helped make the events stronger or more likely.
But for some events in other regions, the analyses that scientists
conducted could not identify a linkage. For a few events, greenhouse
gases actually made the extreme event less likely.
Three independent studies which examined Pacific Sea surface
temperatures and atmospheric anomalies, found some, but not conclusive,
evidence for the impact of human-caused climate change on the ongoing
rainfall deficit in the US state of California. For example, one paper
found evidence that atmospheric pressure patterns related to the drought
increased due to human causes, but their exact influence on the
California drought remains uncertain.
So, in your view, which weather events are more likely to be influenced by human factors than others?
Three papers with different methodologies looking at the Chinese, Korean
and Japanese heat waves reached the same conclusion. This is a very
powerful message. If increases in greenhouse gases are making an event
more likely, then it implies that we should expect events like that more
often in the future.
If some extreme weather events could be linked directly to climate
change, what does this tell us about the urgency to tackle the issue?
It tells us that climate change is not just in the future but, for
example, for the people in eastern China, Korea and Japan, climate
change is in their own backyards.
Thomas C. Peterson is President of World Meteorological
Organization's Commission for Climatology and the Principal Scientist at
the National Climatic Data Center of the National Oceanic and
Atmospheric Administration (NOAA) in the United States.
(C) 2014 Deutsche Welle TV Berlin/Germany