by Mei Wang, Director, Planetary Boundaries Initiative
Those of us in the United Kingdom have come to accept that the weather in this country will be inclement. We get 3 to 4 months of decent warm weather at best and the rest of the year we suffer whatever the climate throws at us.
However, in the last decade, this has been slowly changing. The highest temperature on record for summer was recorded in 2003 at 38.5°C and several years later in 2010, we saw two spells of severe winter weather. This summer the country experienced one of the coolest months of June since 1991 with temperatures struggling to get above 20°C during the day combined with the wettest month of June for last 150 years.
Around the rest of the world, we read dramatic headlines of hay bales exploding in searing temperatures in the US in yet another temperature record breaking summer, serious flooding in parts of Asia (Thailand & Japan) and in various parts of the world (most notably the French Riviera), unusually large numbers of jellyfish which some suggest is partly due to the change in the global climate leading to warmer waters and more conducive breeding conditions for these animals.
Climate change is one of the nine planetary boundaries which scientists claim has been transgressed and these events certainly lend weight to their findings. According to the Stockholm Resilience Centre’s 2009 Report (Planetary Boundaries : Exploring the Safe Operating Space for Humanity), transgressing the earth’s climate change boundary is based on various interdependent tipping points such as “the weakening or reversal of terrestrial carbon sinks, for example, through the ongoing destruction of the world’s rainforests”. Scientists led by Johan Rockström, the Lead Director of the 2009 Report, found that global greenhouse gas emissions in 2009 had already exceeded the recommended level of 350 ppm CO₂and in 2011, evidence shows CO₂ levels have increased to 390 ppm, well above the threshold.
The question is how far can the levels of CO₂ rise before we reach the point of irreversible climate change on this earth and can it be proven that extreme weather events are the result of human activities? Climatologists had predicted 30 years ago that the “warming of the Earth would be most prominent at the poles”. One very visible sign of this is the rapid melting of Arctic ice shelves where tests of ancient air bubbles trapped in the ice cores reveal carbon monoxide levels in the atmosphere today is highest at any time in the last 40,000 years.
There is growing support for the proposition that the changing weather patterns can be attributed to human induced climate change. The latest 22nd State of the Climate Report by the American Meteorological Society, found that 2011 saw some of the most extreme weather events on record such as :
- Southern United States and northern Mexico: Historic drought
- Above‐average North Atlantic hurricane season
- Devastating floods in Brazil
- Worst floods since 1942 in Thailand
- Record destruction by tornadoes in the United States
- Longest cold snap since 1945 in North Korea
- Worst heat wave since 2003 in Central and southern Europe
- Australia was struck by most powerful tropical cyclone, Yasi, since 1918
The report also found that Arctic temperatures in 2011 rose more than two times faster than at lower latitudes and combined with below-normal summer snowfall led to continued patterns of “extreme surface melting”.
“Currently, attribution of single extreme events to anthropogenic climate change remains challenging (Seneviratne et al. 2012),” admitted Peterson, Stott and Herring in an article for the AMS Journal (Volume 93, Issue 7 (July 2012)) as not all extreme weather events could be attributed to climate change. “However, scientific thinking on this issue has moved on and now it is widely accepted that attribution statements about individual weather or climate events are possible, provided proper account is taken of the probabilistic nature of attribution (Nature Publishing Group 2011)”.
Therefore, while the nature of the evidence is only based on probabilities and the application of “event attribution”, it is possible to conclude for example, that the odds of the winter of 2010/2011 in the UK have halved as a result of human influence on the weather and it is 60 times more likely to achieve the warm November 2011 temperatures.
As we continue to see weather extremes all around the world, the assumptions in the State of the Climate Report appear to accord with that in Johan Rockström et al’s reply to critics of the Planetary Boundaries theory where he proposes clear interactions between the transgression of the nitrogen-phosphorus boundaries which potentially erode the resilience of marine ecosystems which in turn reduce their capacity to absorb carbon dioxide and affect the climate change boundary. While changes to the global climate is inevitable, it is likely from the scientists findings there will be more extreme weather events resulting from human activities to come.