What Causes Global Warming

2020 vision

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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.

References


  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. http://dx.doi.org/10.1038/s41558-020-0883-0

  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. http://dx.doi.org/10.1038/s41558-020-0797-x

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