The definitive CO2/CH4 comparison post

There is a new push to reduce CH4 emissions as a possible quick ‘win-win’ for climate and air quality. To be clear this is an eminently sensible idea – as it has been for decades (remember the ‘Methane-to-markets’ initiative from the early 2000s?), but it inevitably brings forth a mish-mash of half-remembered, inappropriate or out-of-date comparisons...

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Forced responses: Sep 2021

A bimonthly open thread for discussions related to climate solutions. Note that open discussions of climate science are here. Possible topics of interest are the trial carbon-capture effort in Iceland and the discussions in the lead up to COP26. Please be constructive and substantive. The post Forced responses: Sep 2021 first appeared on RealClimate.

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Unforced Variations: Sep 2021

This month’s open thread for climate science topics. Not sure about you, but we are still reading the details of the IPCC report.  We are watching the unfolding hurricane season with trepidation, with particular concern related to the impacts of compound events (and not just those associated with climate), and anticipating another low, if not record,...

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Sea level in the IPCC 6th assessment report (AR6)

My top 3 impressions up-front: The sea level projections for the year 2100 have been adjusted upwards again. The IPCC has introduced a new high-end risk scenario, stating that a global rise “approaching 2 m by 2100 and 5 m by 2150 under a very high greenhouse gas emissions scenario cannot be ruled out due to deep uncertainty in ice sheet...

Aug 2021

A deep dive into the IPCC’s updated carbon budget numbers

Guest post by Joeri Rogelj (Twitter: @joerirogelj) Since temperature targets became international climate goals, we have been trying to understand and quantify the implications for our global emissions. Carbon budgets play an important role in this translation. Carbon budgets tell us how much CO2 we can emit while keeping warming below...

Aug 2021

Deciphering the ‘SPM AR6 WG1’ code

I followed with great interest the launch of the sixth assessment report Working Group 1 (The Physical Science Basis) from the Intergovernmental Panel on Climate Change (IPCC) on August 9th.  The main report is quite impressive (see earlier posts here, here, here, and here) but the press conference didn’t come across as being focused and well-prepared....

Aug 2021

A Tale of Two Hockey Sticks

Two decades ago, the so-called “Hockey Stick” curve, published in 1999 by me and my co-authors (Mann, Bradley and Hughes, 1999), was featured in the all-important “Summary for Policy Makers” (SPM) of the 2001 IPCC Third Assessment report. The curve, which depicted temperature variations over the past 1000 years estimated from “proxy data such as tree...

Aug 2021

AR6 of the best

Half a dozen takeaways from a first read of the new IPCC AR6 report. As climate scientists we tend to look at the IPCC reports a little differently than the general public might. Here are a few things that mark this report out from previous versions that relate to issues we’ve discussed here before: Extreme events are increasingly connected...

Aug 2021

#NotAllModels

The biggest contribution scientists can make to #scicomm related to the newly released IPCC Sixth Assessment report, is to stop talking about the multi-model mean. We’ve discussed the issues in the CMIP6 multi-model ensemble many times over the last couple of years – for instance here and here. There are two slightly contradictory features...

Aug 2021

We are not reaching 1.5ºC earlier than previously thought

Guest commentary by Malte Meinshausen, Zebedee Nicholls, and Piers Forster Of all the troubling headlines emerging from the release of the Intergovernmental Panel on Climate Change (IPCC) WG1 report, one warning will surely dominate headlines in the next days and weeks: Earth is likely to reach the crucial 1.5℃ warming limit in the early 2030s....

Aug 2021