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Dr. Zeke Hausfather Profile picture
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23 Dec, 4 tweets, 2 min read
Some cautious climate optimism to end the year from @jtemple in @techreview. We are still far from meeting Paris goals, but the pace of replacing fossil fuels with clean energy has dramatically accelerated in recent years. technologyreview.com/2021/12/23/104…
A decade ago the world appeared on track for a hellish 4C or 5C warming. Today climate policy and technology have flattened that down to around 2.7C (2C-3.6C). carbonbrief.org/analysis-do-co…
This is still a potentially dire future for many human and natural systems – and uncertainties in the climate response to our emissions are decidedly not our friend! – but its much easier to see a path forward to well-below 2C than it was a decade ago.
Or, as @JesseJenkins succinctly puts it,

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More from @hausfath

Dr. Zeke Hausfather Profile picture
15 Dec
Theres a big debate over reforming net metering for residential solar in California happening right now. Its a complex issue, but there are real equity concerns with the current system and – at least in principal – we could find a more effective way to subsidize solar.

A thread:
Its pretty clear the current system has some major problems – its subsidizes higher-income households at the expense of poorer renters and those who cannot afford solar. energyathaas.wordpress.com/2018/03/26/why…
Specifically, the way net metering works is that as a residential solar producer I get to effectively run my meter backwards, getting paid for any generation at my average electricity price (say, at 18 cents per kWh).
Read 12 tweets
Dr. Zeke Hausfather Profile picture
11 Dec
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…
Read 5 tweets
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

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