Three key reports on global warming from the Intergovernmental Panel on Climate Change (IPCC) – the first for six years – should provide sustained justification for further action to reduce greenhouse gases.
The IPCC’s last report, in 2007, led to 157 new climate policies being implemented in the following two years. The September report will update on recent climate change, providing further evidence that scientific indicators and weather extremes are moving in a manner consistent with global warming.
September’s report will be followed by two others, in March and April 2014: “Impacts, Adaptation & Vulnerability” and “Mitigation of Climate Change”.
Land temperatures have become more extreme since 2007. In the Northern Hemisphere, during the decade from 1951, only 1 per cent of the land area was exposed to temperatures higher than three standard deviations from the 1951-1980 mean. However, in 2001-2011, some 11 per cent of land had such high exposure and 1 per cent – an area twice the size of France – incurred heat extremes of five standard deviations from the mean. The same trend is true in the Southern Hemisphere.
The global average temperature has risen by around 0.8C since pre-industrial levels. In July 2013, the World Meteorological Organization noted: “The first decade of the 21st century was the warmest decade recorded since modern measurements began around 1850.”
But despite this, climate sceptics have re-emerged, claiming there has been a hiatus in warming. Our view – consistent with a 97 per cent consensus of scientists – is that warming is still happening.
In 2010 the cost of damages related to floods and droughts was USD52 billion
Notwithstanding advances in climate science though, there is still no single agreed model for predicting how the interplay of forces affecting the Earth’s energy balance will translate into temperature changes. The IPCC reports should present a range of long-term forecast temperature outcomes based on different assumptions.
Scientists use 10 main indicators to determine the extent of climate change, from sea temperatures and snowfall to specific humidity and sea-level changes. And all 10 are trending in the direction associated with warming.
The number of extreme events such as droughts, floods and wildfires has increased broadly in line with the temperature rises since the 1950s. And the costs have escalated from around USD59 billion during the 1980s to USD252 billion in the 1990s and USD190 billion in the 2000s. In 2010 the cost of damages related to floods and droughts was USD52 billion.
Scientists have turned to assessing the attribution of climate change to weather events. This allows policymakers, insurers, electricity providers and other businesses to adapt to climate changes as scientists identify the likelihood of events occurring more frequently.
Science has been crucial for shaping the policy agenda. The first IPCC assessment report was published in 1990 but there was a rise in policy introduction in 1999, three years after the second report, and again in 2008 after the fourth report.
Most of the 157 new policies that followed the 2007 report were in Europe, prior to the Copenhagen summit on climate change. We expect another pick-up in policy introduction focussed on carbon and also factors such as air pollution and health, changing economic structure and water constraints.
The assessment reports have not been without fault. Working with a large number of authors leaves room for error and potential for climate sceptics to discredit the science, as happened after the 2007 report. Nevertheless, the new reports remain important for bridging the gap between science, policy and business, and for generally furthering climate-change knowledge.
The latest IPCC reports will provide justification for action to reduce greenhouse gases. They include submissions from top scientists, a global collaboration of five years’ work. However, there is a risk that, in seeking a consensus between scientists, conclusions are diluted, giving climate change sceptics more leverage.
This research was first published on 1 August 2013.