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Dr. Zeke Hausfather Profile picture
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11 Dec, 5 tweets, 2 min read
Tornadoes are, unfortunately, one of the extreme events where we have the least ability to attribute specific occurrences (or even long-term trends) to climate change. The absence of evidence is not the evidence of absence, but some caution is warranted: carbonbrief.org/tornadoes-and-…
For example, there is little detectable trend in the number of notable (F1+) tornadoes over the past 70 years.
There has been an increase in the number of tornado clusters, but the link between that and changing climate conditions is unclear: science.org/doi/full/10.11…
More broadly, while studies suggest that the frequency and intensity of severe thunderstorms in the US could increase as climate changes, particularly over the US Midwest and Southern Great Plains during spring, "confidence in the model projections is low" according to the NCA4.
This is an area of very active research, but for the time being its too premature to be able to attribute the role of climate changes in specific events like these:

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Dr. Zeke Hausfather Profile picture
7 Dec
Mining is an unavoidable part of a clean energy transition, but impacts can be minimized. All energy alternatives come at a cost: biofuels displace farmland / drive deforestation.
The question should not be "is there an impact", but "is it substantially better than fossil fuels"
For more on these challenges, see this excellent piece by my colleague @juzel_lloyd: thebreakthrough.org/issues/energy/…
"Mining is not a ‘clean’ business and by its very nature, there will always be some alteration to the environment. The real question is this: what are the trade-offs between the damages associated with mining for decarbonization and the damages of not reducing emissions?"
Read 4 tweets
Dr. Zeke Hausfather Profile picture
7 Dec
Climate models are complex physics-based simulations run on the worlds fastest supercomputers.

But there is a quick hack to get results similar to climate models that you can calculate in Excel. Its called the transient climate response to cumulative carbon emissions (TCRE). 1/9
TCRE is the amount of warming as a function of cumulative CO2 emissions. It turns out that warming over time is – to a first order approximation – linearly proportional to cumulative CO2 emissions, as this figure (SPM.10) from the recent IPCC AR6 demonstrates: 2/
As the AR6 notes, "Each 1000 GtCO2 of cumulative CO2 emissions is assessed to likely cause a 0.27C to 0.63C increase in global surface temperature with a best estimate of 0.45C."

Essentially, if you add up CO2 over time and multiply it by 0.45C, you get warming. That simple. 3/
Read 9 tweets
Dr. Zeke Hausfather Profile picture
3 Dec
This sort of language is deeply problematic. A flatting of emissions does not result global warming stopping.

Rather, if emissions are flat global warming continues at its current rate, resulting in a significant rise in global temperature of around 3C by 2100 vs preindustrial.
The only way to stop the world from warming is to get all emissions to (net) zero. The only way to meaningfully cool the planet back down during the next few centuries is to remove more carbon from the atmosphere than we add to it. Image
So while its good news that high-end scenarios where global emissions double or triple are much less likely in a world of falling clean energy prices and a global coal industry in structural decline, emissions still need to fall dramatically to avoid significant future warming.
Read 4 tweets
Dr. Zeke Hausfather Profile picture
29 Nov
The recent IPCC AR6 updated remaining carbon budgets for 1.5C and 2C scenarios.

These budgets let us make simple estimates of when emissions need to reach zero if we allow no net-negative emissions.

1.5C (66%): 2039
1.5C (50%): 2044
2C (66%): 2077
2C (50%): 2088

A thread: 1/8
These are subject to a number of assumptions (and uncertainties), of course. Allowing net-negative emissions expands remaining budgets, while more convex (or concave) emissions pathways would change the date at which zero emissions needs to be reached: 2/
Assumptions around non-CO2 GHG emissions and aerosols also matter. The IPCC provides a best estimate (and uncertainties), but more pessimistic or optimistic assumptions for non-CO2 forcings would reduce or expand the remaining carbon budgets accordingly. 3/
Read 9 tweets
Dr. Zeke Hausfather Profile picture
28 Nov
This is thankfully not true. As we reported in the recent IPCC 6th Assessment Report, scenarios that limit us to around 1.8C (with a 66% chance of avoiding 2C) require getting to net-zero emissions by around 2070, not 2030 as this tweet and article inaccurately imply.
Climate change is a big enough problem to solve that we really don't need disempowering hyperbole like this. Yes, the window to limit warming to 1.5C is rapidly closing, but at the same time below 2C is increasingly within reach.
For reference, here is the SSP1-2.6 scenario that limits warming to ~1.8C by 2100. If you were to exclude the net-negative portion of emissions you would end up closer to 2C by 2100 (or would have to get to net-zero closer to 2060). Either way its a far cry from 2030!
Read 5 tweets
Dr. Zeke Hausfather Profile picture
27 Nov
When it comes to zero emissions, both journey and destination matter.

Warming depends on cumulative emissions, and delaying emissions reductions could result in ~0.15C more warming compared to a linear decline to zero by 2050. Image
If we look at what might be a more plausible pathway given commitments by governments today – zero emissions by 2070 – a slower reduction pathway would result in ~0.25C more warming. Image
These are based on the latest median TCRE value (1.65C per 1000 GtC) from the IPCC AR6. They assume that other forcings (e.g. non-CO2 GHGs and aerosols) remain constant. In more detailed scenarios we generally end up with ~0.05C-0.1C warming in all cases due to non-CO2 forcings.
Read 5 tweets

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