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Dr. Zeke Hausfather Profile picture
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19 Oct, 4 tweets, 1 min read
Winter La Niña is coming. iri.columbia.edu/our-expertise/…
Its decidedly an outlier, but that NASA GMAO model... 🤯
Interesting to compare October 2020 and October 2021 projections, remarkably similar:
(albeit with a slightly more modest La Nina forecast this time around)

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Dr. Zeke Hausfather Profile picture
21 Oct
The US beef industry is trying to deflect their responsibility for methane emissions by claiming that emissions US cows are no longer increasing atmospheric methane concentrations. This is technically true, and completely besides the point.

A quick thread: 1/15
The climate impacts of methane is usually compared with CO2 through the use of Global Warming Potentials (GWPs). There are usefully simple multipliers for a single year's emissions, but provide a misleading impression when applied to emissions over time. 2/
CO2 and methane (CH4) have very different lifetimes. When a ton of CO2 is emitted to the atmosphere, a portion is absorbed quickly, but around 40% remains after a century (and 20% after thousands of years). CH4 is removed much faster, with most gone after 20 years. 3/ Image
Read 15 tweets
Dr. Zeke Hausfather Profile picture
19 Oct
2021 saw the warmest summer for the Earth's land regions, and is on track to be between the 5th and 7th warmest year since records began in the mid-1800s. For an update on temps, models, GHGs, and sea ice see our @CarbonBrief Q3 State of the Climate: carbonbrief.org/state-of-the-c…
Summer land temperatures were relatively flat until 1975, with only around 0.2C warming up to that point. Today, summer land temperatures are around 1.5C above pre-industrial levels, with around 1.3C of that warming happening in just the past 45 years.
NW North America, Eastern Europe, Middle East, Northern Africa, and Siberia all had an exceptionally warm summer. China, sub-Saharan Africa, South America and Australia were modestly above average, while parts of Central America and India were below average.
Read 17 tweets
Dr. Zeke Hausfather Profile picture
15 Oct
There is a weird narrative in some quarters that wind and solar are pure good, while electric vehicles are a necessary (or even unnecessary) evil. This is wrong for many reasons. Yes, we should invest more in public transit and cycle more. We should also be more energy efficient.
But all replacements to fossil fuels will have impacts. Covering 14% of all the US land area with wind and solar farms is potentially doable – but it still has a big impact. EVs are heavier and thus potentially more deadly than ICEs, and batteries are GHG intensive to make.
This does not mean they are not worth doing. We can build much more renewables (and clean firm generation), invest in public transit, replace ICEs and EVs, etc. But if we pretend it will be small and beautiful rather than big and messy we are setting ourselves up for failure.
Read 4 tweets
Dr. Zeke Hausfather Profile picture
15 Oct
One of the biggest long-term impacts of climate change is sea level rise. Even in more moderate emissions scenarios we likely commit the world to many meters of future sea level rise over the next millennium – barring massive anthropogenic carbon removal in future centuries.
The folks at @ClimateCentral have an evocative new visualization of what sea level rise over the next ~1000 years would look like if it happened to cities today. They focus on a 3C warming case – consistent with best estimates of current policy outcomes: picturing.climatecentral.org
Of course, 1000 years is a long time. Who knows what our cities (or species) will look like that far in the future, what actions we might be able to take to slow down or reverse ice sheet loss, or what infrastructure we may build to hold back the rising seas.
Read 4 tweets
Dr. Zeke Hausfather Profile picture
13 Oct
The new @IEA 2021 World Energy Outlook provides more evidence that the world has moved away from high-emissions scenarios where coal powers the 21st century. We still have a long way to go to meet Paris Agreement goals, but are making real progress: thebreakthrough.org/blog/iea-repor… 1/12
The IEA WEO 2021 makes a number of notable changes to its scenarios. It extends its scenarios out to 2050 (vs 2040 in prior reports), and adds a new "announced pledges scenario" (APS) to model mid-century net-zero pledges that have proliferated over the past year. 2/
Heres a comparison of current policy (CPS), stated policy (STEPS), and announced pledges (APS) scenarios over time in the WEO. Note that IEA retired their CPS scenario after 2019, arguing that the world was moving too quickly for a current policy scenario to be of much use. 3/
Read 12 tweets
Dr. Zeke Hausfather Profile picture
12 Oct
Interesting op-ed on geoengineering today by @coralsncaves and @MichaelEMann. Unfortunately, I have to disagree with their suggestion that negative emissions technologies (NETs) are "unlikely to make a meaningful dent in atmospheric CO2". thehill.com/opinion/energy…

A thread: 1/14
In the article they note that IPCC scenarios that peak warming at 1.5C by mid-century later involve substantial drawdown of atmospheric CO2 that prevents further increases in surface temps and is followed by global-scale cooling after emissions go negative. 2/
This is broadly accurate; for example, the new SSP1-1.9 scenario overshoots mid-century resulting in around 1.6C warming, before falling back to 1.4C by 2100 though a very aggressive deployment of net-negative emissions: 3/
Read 14 tweets

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