Our State of the Climate 2020 is live! carbonbrief.org/state-of-the-c…

⬆ Surface temps tied w/ 2016 as warmest
⬆ Record high land temps
⬆ Record ocean heat content
⬆ 1st or 2nd highest troposphere temps
⬆ Record high GHGs
⬆ Sea level
⬇ Glaciers
⬇ Sea ice
⬇ Likely 2021 temps
Global surface temps were between 1.2C and 1.3C above preindustrial levels across the various groups for 2020. NASA had it as the warmest, others have it as 2nd warmest, but in all cases the difference with 2016 (< 0.03C) is smaller than the measurement uncertainty (~0.05C): (2)
We also include a raw temp record based on GHCNv4 land data and ICOADS (HadSST3 raw) ocean data (black dashed line). It shows similar warming to preindustrial, and that warming since preindustrial does not depend on adjustments to the data. (3) carbonbrief.org/explainer-how-…
If we zoom in on 1970-2020 period, we see strong agreement between most surface records in recent decades. Note that in this SotC we've replaced HadCRUT4 with new HadCRUT5 dataset and retired Cowtan & Way (which is substantially similar to HadCRUT5): carbonbrief.org/analysis-why-t… (4)
The past 6 years (2014-2020) really stand out as notably warmer than any prior years. This figure from @RARohde shows the Berkeley Earth 2020 results and its uncertainty (represented by the bell curve) compared to other years: (5)
Global temps obscure larger regional changes. For example, while the globe as a whole has warmed by around 1.2C to 1.3C, land areas have warmed close to 2C and oceans only 1C since preindustrial times: (6)
Some parts of the world were much warmer in 2020 than others; we saw particularly high temperatures in the Arctic, over Siberia, Europe, Central and South America, the Middle East, the northern Pacific Ocean and the Antarctic Ocean: (7)
A sizable portion of the Earth's surface saw record warm temperatures, while no location on Earth saw record cold (or even top 5 cold conditions) for the year as a whole: (8)
Surface temperatures were pretty dead on in climate model projections in 2020. Here are results from the last generation of climate models (CMIP5) for 1850-2100, along with observations (colored lines): (9)
The climate model fields used here are "blended"; that is, they combine surface air temps over land with sea surface temps over the oceans to mimic the way we take observations. If we just use surface air temps models are a bit warmer in recent years: (10)
We also have a new generation of climate models – CMIP6 – that are being run. Using the 33 models currently available (for historical and SSP2-4.5) we can compare observations and CMIP6 models (note that blended CMIP6 fields are not yet available): (11)
CMIP6 models are on average running a tad warmer than observations in recent years, likely reflecting the higher climate sensitivity of some of the models compared to CMIP5. For more on these new climate models, see our Carbon Brief explainer: carbonbrief.org/cmip6-the-next… (12)
The two lower troposphere temperature records (e.g. ~5 km up in the atmosphere) show 2020 as the warmest (RSS) and second warmest (UAH) on record. Note that El Nino and La Nina conditions tend to amplify troposphere temps more than on the surface: (13)
Ocean heat content set a new record in 2020. More than 90% of heat trapped by greenhouse gases accumulated in oceans, and unlike atmosphere (which is more variable) nearly every year on the oceans set a new record. Most heat has accumulated in the upper (0-700m) ocean. (14)
Sea level rise continues upward, with nearly every year seeing higher sea levels. There is evidence that sea level rise is accelerating, driven by melting glaciers and ice sheets. Note that data is not yet available to the end of 2020, so this figure goes through 2019. (15)
Global glacier mass loss continues, and has accelerated in recent years. Similar to the sea level figure, this one only goes through the end of 2019 as full 2020 data is not available yet. (16)
Atmospheric GHG concentrations (CO2, CH4, N2O) all reached record levels in 2020 despite some emissions reductions due to COVID-19. Because they accumulate in the atmosphere, a single yearly reduction in emissions will not cause concentrations to fall: (17)
Arctic sea ice was at record low daily levels for much of the summer in 2020. The summer minimum (lowest point of the year) was the second lowest on record after 2012: (18)
As a result, the Northeast Passage was open for shipping in 2020 for longer than any other year: (19)
The fact that 2020 was tied as the warmest year on record is all the more remarkable given that the prior record (2016) was a super El Nino year, while 2020 had a modest La Nina event in the second half of the year (20)
La Nina tends to result in cooler global temps, and likely contributed to a bit cooler conditions over the past few months. However, the largest effect of current La Nina conditions will be felt in 2021, which various groups expect to be cooler than 2020: (21)
What matters for the climate is not the leaderboard of individual years. Rather, it is the long-term upward trend in global temperatures driven by human emissions of greenhouse gases. Until the world reduces emissions down to net-zero, the planet will continue to warm. (22)

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More from @hausfath

14 Jan
Remember the 15-year "hiatus" in global warming?

Turns out the last 15 years (2006-2020) were twice as far above the long term trend as the hiatus (1998-2012) was below it.

Lets not over-interpret short-term variability, but perhaps its time to start talking about acceleration Image
It is important to emphasize that some of the discussion of the "hiatus" was driven by observational data artifacts (lack of arctic coverage, biases due to the transition from ships to buoys for ocean measurements) that have now been corrected.
That said, there is growing evidence that the rate of warming has accelerated in recent years.

1970-2020: 0.19C per decade
1998-2012: 0.13C per decade
2006-2020: 0.31C per decade

The next few years will be quite important to watch.
Read 4 tweets
12 Jan
Michael Mann has new book out – The New Climate War. I've coauthored papers in the past with Mike and respect his scientific and communications work. However, in his book he claims that my organization @TheBTI was "initially linked to the fossil fuel industry". This is false. (1)
Prior to the release of his book we reached out and sent the following letter to Mike, giving him the opportunity to correct the record. Unfortunately, as we never heard back we have decided to make it public: thebreakthrough.org/articles/lette… (2)
The @TheBTI has never accepted any money from the fossil fuel industry or industry employees. Mike suggests otherwise based on the fact that BTI once received some funding from the George and Cynthia Mitchell Foundation. thebreakthrough.org/about/who-we-a… (3)
Read 12 tweets
11 Jan
One of the under-appreciated aspects of the Chinese 2060 net-zero target is the massive spillover effects it would have on the rest of the world. An economy as large as China's mobilizing to decarbonize the entire economy would substantially drive down clean energy costs. 1/6
The recent IEA WEO 2020 predicts that global CO2 emissions will plateau around 2019 levels, but does not include recent net-zero targets. Including China's (via the Tsinghua University analysis) would lead to global emissions declining in coming years: 2/6
If China were to decarbonize while the rest of the world did nothing, it alone would drive global solar prices down by 65% and wind prices down by 17% assuming historical learning rates continue. These effects will be even more pronounced for nascent tech outside power sector 3/6
Read 6 tweets
7 Jan
If we can get emissions down to zero (or net-zero), the planet will likely stop warming. Good @guardian piece covering this issue – which is well understood by the scientific community but often missed in public discussions. theguardian.com/environment/20… 1/6
This is good news, because it means that warming that occurs this century is almost entirely under our control. We can decided how much CO2 and other greenhouse gases we emit, and the climate will respond accordingly. 2/6
However, the downside of this finding is that even if we get emissions all the way down to zero, temperatures will not fall, at least for the next few centuries. Without net-negative emissions climate change is largely irreversible. 3/6
Read 6 tweets
5 Jan
Lets clarify something about "committed warming". A world where concentrations of CO2 and other GHGs remain constant in the atmosphere is not the same as a world where emissions go to zero. The former has ~0.5C or more warming "in the pipeline", while the latter is closer to 0C.
If concentrations stay constant (e.g. atmospheric CO2 remains at 412 ppm indefinitely), the oceans continue to heat up for the next few millennia. The vast heat capacity of the deep oceans currently buffers warming, as some of the heat diffuses down to the deep ocean.
If emissions actually fall all the way to zero (or net-zero), atmospheric CO2 concentrations start declining. This mostly counteracts the warming in the pipeline as the oceans continue to warm to reach equilibrium. agupubs.onlinelibrary.wiley.com/doi/full/10.10… Image
Read 7 tweets
4 Jan
Fascinating new paper by @AndrewDessler and colleagues arguing committed warming might be higher than expected given historical pattern effects. Its combining a lot of different concepts together, so lets spend some time disentangling them nature.com/articles/s4155…

A thread: 1/19
The paper's headline number is that we previously thought the world was committed to 1.3C warming, but that number is actually over 2C (> 1.5C by 2100). This is quite a different message than we get from Earth System Models, which suggest committed warming is only ~1.2C. 2/19
This would imply that the 1.5C by 2100 target is effectively impossible, and that long-term warming of >2C would be very difficult to avoid. However, the devil is in the details, and the picture is not quite as dire as it would seem at first glance. 3/19
Read 19 tweets

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