The UN’s Intergovernmental Panel on Climate Change (IPCC) is preparing its latest Assessment Report (AR5) on the state of climate science, and is having to iron out disagreements between its scientist members. The vast majority of scientists agree that the Earth is warming, and that humans are culpable to some degree do to greenhouse gas emissions. But that’s where the consensus ends—climate models failed to predict a slowdown in warming in recent years, and climate scientists can’t agree on why. And, as the NYT reports, they’re struggling to agree on specific predictions for sea level and temperature rise in the latest IPCC report:
In one case, we have a lot of mainstream science that says if human society keeps burning fossil fuels with abandon, considerable land ice could melt and the ocean could rise as much as three feet by the year 2100. We have some outlier science that says the problem could be quite a bit worse than that, with a maximum rise exceeding five feet.The drafters of the report went with the lower numbers, choosing to treat the outlier science as not very credible.In the second case, we have mainstream science that says if the amount of carbon dioxide in the atmosphere doubles, which is well on its way to happening, the long-term rise in the temperature of the earth will be at least 3.6 degrees Fahrenheit, but more likely above 5 degrees. We have outlier science that says the rise could come in well below 3 degrees.In this case, the drafters of the report lowered the bottom end in a range of temperatures for how much the earth could warm, treating the outlier science as credible.
You can almost see the Grey Lady shaking her head at panel’s inconsistency here: on sea level rise, they went with the more conservative mainstream numbers, but on temperature rise, they went with the more conservative fringe predictions. But there is a common thread in both decisions: given the flack the panel’s last report got for overstating its case and the recent warming plateau, it’s possible that the IPCC is making a conscious decision to err on the side of caution with AR5.These quibbles are another reminder—as if we needed one—that our understanding of climate is still quite limited. Assigning specific numbers and narrow ranges to outcomes years down the road have already proved fiendishly difficult. It’s no surprise then that the IPCC is split on two key components of their upcoming report. These reports have always been at least as political as they are scientific.[Earth image courtesy of NASA ESA]