“Unequivocal” and “unprecedented”: IPCC synthesis report sets out the evidence on climate change

“Human influence on the climate system is clear and growing, with impacts observed on all continents. If left unchecked, climate change will increase the likelihood of severe, pervasive and irreversible impacts for people and ecosystems.”

So concludes the newly published synthesis report of the Intergovernmental Panel on Climate Change (IPCC), released this weekend in Copenhagen. The report represents the final stage of the IPCC’s fifth assessment report, drawing together the findings of the three Working Groups – The Physical Science Basis; Impacts, Adaptation and Vulnerability; and Mitigation – to produce a concise summary of the latest and most comprehensive assessment of climate change. In the words of IPCC Chair Rajendra Pachauri, it is anticipated that the report “will provide the roadmap by which policymakers will hopefully find their way to a global agreement to finally reverse course on climate change”.

The summary for policymakers, perhaps the most important version of the report, makes for sobering reading. It states that warming of the climate system is “unequivocal”, with many of the observed changes “unprecedented”. Anthropogenic greenhouse gas emissions are now “higher than ever”, and their effects are “extremely likely” to be the dominant cause of observed warming. For all emissions scenarios other than strong mitigation, the increase in surface temperature above pre-industrial levels is “more likely than not” to exceed 2°C by the end of the century, with increased likelihood of “severe, pervasive and irreversible impacts for people and ecosystems”.

If we focus specifically on the ecological content, the report states with high confidence that “many terrestrial, freshwater and marine species have shifted their geographic ranges, seasonal activities, migration patterns, abundances and species interactions in response to climate change”. It is clear that climate change will amplify existing risks and create new risks in natural systems, with a “large fraction of species” facing “increased extinction risk” during and beyond the 21st century. The report draws specific attention to the vulnerability of coral reefs and polar ecosystems, and also highlights the inability of plant species in particular to shift their geographic range quickly enough to keep pace with both current and projected rates of climate change.

Taken alongside the impacts on other physical systems, including ice sheet melting, an increase in extreme weather events, sea-level rise and ocean acidification, and the consequent effects on food security and ecosystem services, the outlook appears bleak. And indeed, the message is set out in stark terms, emphasising that without stronger mitigation efforts now, including rapid cuts to carbon emissions, there is a “very high risk of severe, widespread and irreversible impacts”. Yet the report also offers hope; according to Rajendra Pachauri “we have the means to limit climate change. The solutions are many and allow for continued economic and human development. All we need is the will to change”.

The next twelve months will provide a crucial test of that will. In late 2015 the 21st Conference of Parties to the United Nations Framework Convention on Climate Change (UNFCCC) will meet in Paris, with the aim of securing a universal, legally binding agreement on climate change and emissions reduction from all nations in the world for the first time. The IPCC synthesis report represents a clear platform from which evidence-based negotiations can proceed; ensuring that those negotiations succeed in reaching the necessary agreement remains a complex and uncertain task.