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Unforced Variations: Mar 2021

Filed under: — group @ 1 March 2021

This month’s open thread. Northern Hemisphere Spring is on it’s way, along with peak Arctic/minimum Antarctic sea ice, undoubtedly more discussion about the polar vortex, and the sharpening up of the (currently very uncertain) ENSO forecast for the rest of this year.

2020 Hindsight

Yesterday was the day that NASA, NOAA, the Hadley Centre and Berkeley Earth delivered their final assessments for temperatures in Dec 2020, and thus their annual summaries. The headline results have received a fair bit of attention in the media (NYT, WaPo, BBC, The Guardian etc.) and the conclusion that 2020 was pretty much tied with 2016 for the warmest year in the instrumental record is robust.

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2020 vision

A meeting of smoke and storms (NASA Earth Observatory)

No-one needs another litany of all the terrible things that happened this year, but there are three areas relevant to climate science that are worth thinking about:

  • What actually happened in climate/weather (and how they can be teased apart). There is a good summary on the BBC radio Discover program covering wildfires, heat waves, Arctic sea ice, the hurricane season, etc. featuring Mike Mann, Nerlie Abram, Sarah Perkins-Kilpatrick, Steve Vavrus and others. In particular, there were also some new analyses of hurricanes (their rapid intensification, slowing, greater precipitation levels etc.), as well as the expanding season for tropical storms that may have climate change components. Yale Climate Connections also has a good summary.
  • The accumulation of CMIP6 results. We discussed some aspects of these results extensively – notably the increased spread in Equilibrium Climate Sensitivity, but there is a lot more work to be done on analyzing the still-growing database that will dominate the discussion of climate projections for the next few years. Of particular note will be the need for more sophisticated analyses of these model simulations that take into account observational constraints on ECS and a wider range of future scenarios (beyond just the SSP marker scenarios that were used in CMIP). These issues will be key for the upcoming IPCC 6th Assessment Report and the next National Climate Assessment.
  • The intersection of climate and Covid-19.
    • The direct connections are clear – massive changes in emissions of aerosols, short-lived polluting gases (like NOx) and CO2 – mainly from reductions in transportation. Initial results demonstrated a clear connection between cleaner air and the pandemic-related restrictions and behavioural changes, but so far the impacts on temperature or other climate variables appear to be too small to detect (Freidlingstein et al, 2020). The impact on global CO2 emissions (LeQuere et al, 2020) has been large (about 10% globally) – but not enough to stop CO2 concentrations from continuing to rise (that would need a reduction of more like 70-80%). Since the impact from CO2 is cumulative this won’t make a big difference in future temperatures unless it is sustained through post-pandemic changes.
    • The metaphorical connections are also clear. The instant rise of corona virus-denialism, the propagation of fringe viewpoints from once notable scientists, petitions to undermine mainstream epidemiology, politicized science communications, and the difficulty in matching policy to science (even for politicians who want to just ‘follow the science’), all seem instantly recognizable from a climate change perspective. The notion that climate change was a uniquely wicked problem (because of it’s long term and global nature) has evaporated as quickly as John Ioannidis’ credibility.

I need to take time to note that there has been human toll of Covid-19 on climate science, ranging from the famous (John Houghton) to the families of people you never hear about in the press but whose work underpins the data collection, analysis and understanding we all rely on. This was/is a singular tragedy.

With the La Niña now peaking in the tropical Pacific, we can expect a slightly cooler year in 2021 and perhaps a different character of weather events, though the long-term trends will persist. My hope is that the cracks in the system that 2020 has revealed (across a swathe of issues) can serve as an motivation to improve resilience, equity and planning, across the board. That might well be the most important climate impact of all.

A happier new year to you all.


  1. P.M. Forster, H.I. Forster, M.J. Evans, M.J. Gidden, C.D. Jones, C.A. Keller, R.D. Lamboll, C.L. Quéré, J. Rogelj, D. Rosen, C. Schleussner, T.B. Richardson, C.J. Smith, and S.T. Turnock, "Current and future global climate impacts resulting from COVID-19", Nature Climate Change, vol. 10, pp. 913-919, 2020.
  2. C. Le Quéré, R.B. Jackson, M.W. Jones, A.J.P. Smith, S. Abernethy, R.M. Andrew, A.J. De-Gol, D.R. Willis, Y. Shan, J.G. Canadell, P. Friedlingstein, F. Creutzig, and G.P. Peters, "Temporary reduction in daily global CO2 emissions during the COVID-19 forced confinement", Nature Climate Change, vol. 10, pp. 647-653, 2020.

Does a slow AMOC increase the rate of global warming?

Filed under: — stefan @ 18 July 2018

Established understanding of the AMOC (sometimes popularly called Gulf Stream System) says that a weaker AMOC leads to a slightly cooler global mean surface temperature due to changes in ocean heat storage. But now, a new paper in Nature claims the opposite and even predicts a phase of rapid global warming. What’s the story?

By Stefan Rahmstorf and Michael Mann

In 1751, the captain of an English slave-trading ship made a historic discovery. While sailing at latitude 25°N in the subtropical North Atlantic Ocean, Captain Henry Ellis lowered a “bucket sea-gauge” down through the warm surface waters into the deep. By means of a long rope and a system of valves, water from various depths could be brought up to the deck, where its temperature was read from a built-in thermometer. To his surprise Captain Ellis found that the deep water was icy cold.

These were the first ever recorded temperature measurements of the deep ocean. And they revealed what is now known to be a fundamental feature of all the world oceans: deep water is always cold. The warm waters of the tropics and subtropics are confined to a thin layer at the surface; the heat of the sun does not slowly warm up the depths as might be expected. Ellis wrote:

“This experiment, which seem’d at first but mere food for curiosity, became in the interim very useful to us. By its means we supplied our cold bath, and cooled our wines or water at pleasure; which is vastly agreeable to us in this burning climate.”

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El Niño and the record years 1998 and 2016

Filed under: — stefan @ 4 November 2017

2017 is set to be one of warmest years on record. Gavin has been making regular forecasts of where 2017 will end up, and it is now set to be #2 or #3 in the list of hottest years:

In either case it will be the warmest year on record that was not boosted by El Niño. I’ve been asked several times whether that is surprising. After all, the El Niño event, which pushed up the 2016 temperature, is well behind us. El Niño conditions prevailed in the tropical Pacific from October 2014 throughout 2015 and in the first half of 2016, giving way to a cold La Niña event in the latter half of 2016. (Note that global temperature lags El Niño variations by several months so this La Niña should have cooled 2017.) More »

O Say Can You CO2…

Filed under: — group @ 12 October 2017

Guest Commentary by Scott Denning

The Orbiting Carbon Observatory (OCO-2) was launched in 2014 to make fine-scale measurements of the total column concentration of CO2 in the atmosphere. As luck would have it, the initial couple of years of data from OCO-2 documented a period with the fastest rate of CO2 increase ever measured, more than 3 ppm per year (Jacobson et al, 2016;Wang et al, 2017) during a huge El Niño event that also saw global temperatures spike to record levels.

As part of a series of OCO-2 papers being published this week, a new Science paper by Junjie Liu and colleagues used NASA’s comprehensive Carbon Monitoring System to analyze millions of measurements from OCO-2 and other satellites to map the impact of the 2015-16 El Niño on sources and sinks of CO2, providing insight into the mechanisms controlling carbon-climate feedback.

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  1. J. Wang, N. Zeng, M. Wang, F. Jiang, H. Wang, and Z. Jiang, "Contrasting terrestrial carbon cycle responses to the two strongest El Niño events: 1997–98 and 2015–16 El Niños", 2017.
  2. J. Liu, K.W. Bowman, D.S. Schimel, N.C. Parazoo, Z. Jiang, M. Lee, A.A. Bloom, D. Wunch, C. Frankenberg, Y. Sun, C.W. O’Dell, K.R. Gurney, D. Menemenlis, M. Gierach, D. Crisp, and A. Eldering, "Contrasting carbon cycle responses of the tropical continents to the 2015–2016 El Niño", Science, vol. 358, pp. eaam5690, 2017.

Predicting annual temperatures a year ahead

Filed under: — gavin @ 16 September 2016

I have a post at Nate Silver’s 538 site on how we can predict annual surface temperature anomalies based on El Niño and persistence – including a (by now unsurprising) prediction for a new record in 2016 and a slightly cooler, but still very warm, 2017.

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Australian silliness and July temperature records

Filed under: — gavin @ 16 August 2016

Some of you that follow my twitter account will have already seen this, but there was a particularly amusing episode of Q&A on Australian TV that pitted Prof. Brian Cox against a newly-elected politician who is known for his somewhat fringe climate ‘contrarian’ views. The resulting exchanges were fun:
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Comparing models to the satellite datasets

How should one make graphics that appropriately compare models and observations? There are basically two key points (explored in more depth here) – comparisons should be ‘like with like’, and different sources of uncertainty should be clear, whether uncertainties are related to ‘weather’ and/or structural uncertainty in either the observations or the models. There are unfortunately many graphics going around that fail to do this properly, and some prominent ones are associated with satellite temperatures made by John Christy. This post explains exactly why these graphs are misleading and how more honest presentations of the comparison allow for more informed discussions of why and how these records are changing and differ from models.
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2015 Temperatures

Filed under: — gavin @ 21 January 2016

To no-one’s great surprise, 2015 was clearly a record year in all the surface temperature analyses (GISTEMP, NOAA, HadCRUT4, Cowtan&Way, JMA + Berkeley Earth). There is a lot of discussion of this in the press, and on the relevant websites, so not much to add here. A few figures didn’t make it into the official announcement (audio) though…

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