A research update on climate change has indicated that many global risks are now assessed as stronger than predicted by the 2007 IPCC Fourth Assessment Report (AR4)1. The risk of large sea-level rise, extreme weather events and ocean acidification are all thought to be underestimated by the AR4.
The AR4 is the most complete and respected assessment of scientific knowledge on human-caused climate change and its impacts. Due to its scope and scale, the cut-off date for inclusion of research was between mid-2006 and early 2007. Since then, observations of recent climate change, improved understanding of 'feedback loops' and new projections of future changes have painted a slightly different, and perhaps more serious, picture.
The new study used research published between the finalisation of the AR4 and September 2008 to provide updates on the scientific knowledge of climate change. The IPCC Fifth Assessment Report (AR5) is scheduled to be finalised in 2014.
New observations have been recorded on melting ice sheets and glaciers. For example, Arctic sea ice reached a new all-time minimum in September 2007 and the melting of the Greenland ice sheet established a new record in the summer 2007. Recent studies have improved the understanding of the rate of sea-level rise and the contribution from melting ice sheets. New models based on this knowledge have produced substantially higher figures for sea-level rise than the estimates of the AR4 which did not include ice-sheet dynamics. For example, one model estimated a sea level rise of 55-125 cm by 2100, compared to AR4's prediction of 19-59cm.
Most climate models in the AR4 did not consider physical or biological carbon-cycle feedbacks. These are processes triggered by climate change that can further increase greenhouse gas levels in the atmosphere, such as the melting of permafrost that produces methane. Recent studies have indicated that including all known carbon-cycle feedbacks in models of future climate change substantially increases the estimates of warming. For example, consideration of feedback loops increased the probability of exceeding 2°C warming by 2100 from 10 to 23 per cent for a given emissions scenario.
New research has also shed light on possible tipping elements that might trigger abrupt climate change, such as the collapse of the West Antarctic ice sheet and large-scale dieback of the Amazonian rainforest. For example, the threshold range for global warming that would trigger a radical shrinking or complete melting of the Greenland ice sheet is estimated to be 1.5-2.5°C, rather than 1.9-4.6°C as predicted by the AR4.
Lastly the study investigated recent research on the impacts of climate change on biodiversity hotspots. In particular, recent studies have shown very substantial risks to coral reefs and other marine ecosystems from the combined effects of climate change and the acidification of oceans.
Alongside new observations of increased CO2 concentrations, this update on the risks from global climate change emphasises an increased urgency to implement comprehensive mitigation and adaptation policies.
Source: Füssel, H. (2009). An updated assessment of the risks from climate change based on research published since the IPCC Fourth Assessment Report. Climatic Change. 97:469-482.