E&E news [paywalled] recently tackled the subject of evolving climate science. Reporter Chelsea Harvey examined the five assessment reports from the U.N. Intergovernmental Panel on Climate Change (IPCC), which was established in 1988 by the U.N. Environment Programme and the World Meteorological Organization.
The UN tasked the IPCC with assessing the risks from climate change by using the most up-to-date scientific and technical information. The five IPCC reports since 1988 have grown increasingly complex, with the latest published in 2014 (the sixth is due in 2022).
The bottom line over 30 years? The big picture forecast of climate warming, covering a broad range of potential temperature rise, remains the same:
[M]ajor uncertainties about climate sensitivity remain, even though estimates of its value are largely the same as they were in the 1990s. The First and Fifth assessment reports both suggest that a doubling of atmospheric carbon dioxide would increase global temperatures by between 1.5 and 4.5 C.
But the IPCC has been too conservative on some specific topics, like sea level rise:
The First Assessment Report suggested that sea levels would likely rise by about 65 centimeters by the end of the century, under a business-as-usual trajectory, “mainly due to thermal expansion of the oceans and the melting of some land ice.” By the Fifth Assessment Report in 2014, scientists were projecting up to a meter of sea-level rise by the end of the century under a business-as-usual scenario.
Even in the few years since, multiple studies have suggested that the IPCC’s estimates may be too low, taking into account improvements in scientists’ understanding of the physical processes affecting the world’s ice sheets. Some scientists expect the projections reported in the Sixth Assessment Report will be even higher.
And the IPCC underestimated how much warming has already occurred since 1880:
[W]hile the First Assessment Report estimated that global temperatures have warmed by between 0.3 and 0.6 degree Celsius in the past century, the Fifth Assessment Report honed this estimate to about 0.85 C since 1880.
The science has also improved in terms of modeling capability and ability to forecast impacts in specific parts of the globe, as well as attribute particular weather events to climate change with more precision.
Clearly the science over the past 30 years has been too conservative in some respects, which should give us even more motivation to take action on climate. We’ll need to reduce greenhouse gas emissions as much as we can through clean technology deployment, while preparing for the now-unavoidable impacts to come.
