A while ago, the journal Nature [1] held a survey among the lead authors of one of the recent IPCC reports, the one on the physical science of climate change (Working Group I). The outcome is depicted below. Most IPCC authors expect that we will end up at 3 °C compared to pre-industrial levels, just a few are a bit more optimistic:
Earlier this year, I asked the same question to a group of followers on Twitter with an interest in science and I got about the same result [2]. I do not know what is the background of the respondees’ expectations. Most likely it is based on the many estimates of the impact of the Paris agreement. With some variation, the research into the impact of all the Paris-related commitments came to the conclusion that the combined effect of all commitments would be about 3 °C [3][4].
But this overlooks one important element in the Paris Agreement: the so-called ratchet mechanism. While the Paris Agreement was forged, the negotiators already acknowledged that the total of pledges by the countries was not sufficient. Therefore, it was agreed that every five years countries would be invited to present a new pledge (called Nationally Determined Contribution in the UNFCCC jargon). Each new pledge should be a progression compared to the previous one. There is no way back – therefore the name ratchet mechanism.
The question is of course whether this mechanism really works. The first test was at the Glasgow climate conference in November 2021 – postponed by one year because of Covid-19. And: yes, it worked. Many countries have updated their pledges and come with higher ambitions for 2030; these include China, the USA, Japan, and the European Union. Moreover, these countries and many others have submitted pledges for the phase-out of net greenhouse gas emissions (or just CO2) in 2050 or 2060.
Do all these enhanced pledges make a difference? Also here, the answer is a clear yes, according to the analysis by Climate Action Tracker:
| 2015 Paris Agreement [5] |
2030 pledges | 2.7 °C |
| 2021 Glasgow Pact [6] |
2030 pledges 2030 pledges + net-zero pledges |
2.4 °C 2.1 °C optimistic interpretation: 1.8 °C |
Obviously, if all the countries would live up to their pledges, we are heading rather to 2 °C than to 3 °C by the end of this century. The analysis by Climate Action Tracker is confirmed by a publication in Nature earlier this year: full implementation of all the pledges would lead to limiting global warming to 1.9 – 2.0 °C [7].
The final question is of course: will the countries live up to their pledges? Also here, the historic developments over the past 6 years give way to some optimism. Climate Action Tracker not only assesses the impact of pledges but also the impact of concrete policies. Whereas in 2015, they estimated that actual policies would lead to a temperature increase of 3.6 °C, in their current assessment this has dropped to 2.7 °C. There clearly is a substantial lag between pledges and policy implementation on the ground, but at least we also see substantial progress here.
So, taking it all together: step-by-step we are moving towards pledges and associated policies that will bring us closer to a maximum temperature rise of 2 °C. Don’t interpret this as “we’re done!” Actually getting there will still require a lot of effort for all governments, all companies, and actually all of us in the coming decades.
A global temperature increase of 2 °C is a lot better than 3 °C. However, there is also wide agreement now that the climate change impacts will be still a lot worse at 2 °C than at 1.5 °C. And can we achieve that latter target? As we have shown in the latest IPCC report, the window to reach 1.5 °C is rapidly closing. Whereas reaching 2 °C could be considered a likely outcome of the current progression of international climate action, this step-by-step approach seems just not fast enough for reaching the 1.5 C target. How to get to a 1.5 °C pathway should therefore be the top issue at the table at the next climate conference in Sharm El Sheikh next November.
The ratchet gear on the photograph was found on a steamshovel build around the time of WW1. Photo credit: Pete Muller.
[1] J. Tollefson: Top climate scientists are sceptical that nations can rein in global warming, Nature 599(2021)22-24.
[2] In January I was operating the Twitter account NL_Wetenschap for a week. The Dutch-language account has over 20,000 followers, with presumably a more than average interest in science. I asked the same question as in the Nature article [1]. The response was as follows.
[3] J. Rogelj, M. den Elzen, N. Höhne, T. Fransen, H. Fekete, H. Winkler, R. Schaeffer, F. Sha, K. Riahi, M. Meinshausen: Paris Agreement climate proposals need a boost to keep warming well below 2 °C, Nature 534(2016)631-639.
[4] All temperatures mentioned in this blog are compared to pre-industrial levels. Only mid-range numbers are given, but all numbers show uncertainty, especially due to the uncertainty in the reaction of the climate system to the increased presence of greenhouse gases in the atmosphere.
[5] J. Gütschow, L. Jeffery, R. Alexander, B. Hare, M. Schaeffer, M. Rocha, N. Höhne, H. Fekete, P. van Breevoort, K. Blok: INDCs lower projected warming to 2.7°C – significant progress but still above 2°, Climate Action Tracker, 2015, available here.
[6] See, the “thermometer” on the website of Climate Action Tracker, with link to the methodology section.
[7] M. Meinshausen, J. Lewis, C. McGlade, J. Gütschow, Z. Nicholls, R. Burdon, L. Cozzi, B. Hackmann: Realisation of Paris Agreement pledges may limit warming just below 2 °C, Nature 604(2022)304-309.
