Glen Peters Profile picture
Sep 24, 2020 6 tweets 8 min read Read on X
@IvoHlebarov @PeterGleick @MichaelEMann @JKSteinberger @KHayhoe It is what the IPCC says. The way framed in the thread is not quite correct. Yes, the 50% and net zero 2050 is based on scenarios with carbon dioxide removal. You can do stylised with a carbon budget, and take the numbers from SR15 Table 2.2.
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@IvoHlebarov @PeterGleick @MichaelEMann @JKSteinberger @KHayhoe If we just accept these numbers (& not quibble over temp baselines, feedbacks, etc). These budgets are defined on when emissions reach zero (and temperature is about peak). The IPCC statement is equivalent to 50% 1.5C (at peak).

Area of triangle: 580*2/42=28 years to zero

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@IvoHlebarov @PeterGleick @MichaelEMann @JKSteinberger @KHayhoe Lets say that budget says zero globally in 2045, with absolutely no CO2 removal. If that is the criteria you want, then all countries can emit zero after 2045.

You want 66%, the 420GtCO2 budget? There are no scenarios in the literature, that I know of, that can do that!

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@IvoHlebarov @PeterGleick @MichaelEMann @JKSteinberger @KHayhoe To say it is a dangerous myth will get lots of retweets, but is itself a dangerous myth. I am not sure what the object is? Yes, quite ok to be critical of CO2 removal (as I have), but that is a different issue issue if you ask me.

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@IvoHlebarov @PeterGleick @MichaelEMann @JKSteinberger @KHayhoe And the point here is not to put in criteria which makes 1.5C seem harder & harder. The point is to stay below 1.5C (or well below 2C if you are into Paris). To do that, we need to reduce emissions, probably faster than we realistically could (disagree? Look out the window)

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@IvoHlebarov @PeterGleick @MichaelEMann @JKSteinberger @KHayhoe I will stop there... Otherwise I will just continue on an endless rant...

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More from @Peters_Glen

Nov 13
📢Global Carbon Budget 2024📢

Despite some predicting a peak in global fossil CO2 emissions, we estimate growth of 0.8% [-0.3% to 1.9%] in 2024. Maybe a peak next year?

Is it all bad news, or can we find some good news?

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We estimate EU emissions down 3.8%, US edged down 0.6%, & Chinese emissions edged up 0.2%.

Emissions were up strongly in India 4.6% & international aviation 13.5%.

The record growth in renewables is helping bend the curve, just not enough to get a peak in global emissions.

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Land use change emissions have been edging down the last two decades, but with a slight & uncertain tick up in the last years.

We expect a rise in 2024, driven by fire emissions linked to deforestation & degradation in South America, exacerbated by a temporary El Niño.

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Read 10 tweets
Sep 16
I am still pondering over 2023 & El Nino. Is 2023 an (unusual) outlier or not?

Looking at anomaly in 2023 relative to the trendline (loess 50 year window), without (left) & with (right) annualised ENSO lags, then 2023 is rather mundane.

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When looking at the temperature change relative to the previous year, without (left) & with (right) annualised ENSO lags, then 2023 is more unusual depending on the lag.

If 2023 is unusual, then it could be equally explained by 2022 being low (rather than 2023 being high).

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There are numerous ways to consider ENSO. I have used annualised indexes, & various lags can be included. It is also possible to take sub-annual indexes (eg, several months), & again, various lags.

What is statistically best? I presume there is a paper on this.

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Read 5 tweets
Sep 13
I started to take an interest in the 2023 temperature increase...

The first plot I did, to my surprise, seems to suggest that 2023 is not unusual at all (given El Nino).

Why?

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It all depends on how you slice the data. The previous figure was the anomaly relative to a trend (loess with 50 year window).

If I plot the change from the previous year (delta T), then 2023 is more unusual. Though, still, is it 2023 that is unusual, or 2022, or 2016, or?

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The loess trend changes shape with the data, making the 2023 anomaly smaller. It is also possible to use a linear trend, making the 2023 anomaly larger.

Comparing the anomaly to a linear trend will make 2023 more important (than if loess is used).

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Read 7 tweets
Aug 6
Has the land sink collapsed in 2023?

I am not so convinced. The land sink has a lot of variability, mainly due to El Nino, and an El Nino overlapped 2023. So we expect a lower land sink in 2023.

(My estimate assumes the ocean sink was average).

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Was 2023 an El Nino year? That is not so obvious...

How does one average the monthly sea surface data to an annual value El Nino index? How does one account for the lag between El Nino and the change in atmospheric CO2 growth?

There is no unique answer to this.

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This figure shows the monthly El Nino index annualised with different time lags. 2023 is an El Nino or La Nina, depending on how you average!

@richardabetts & @chrisd_jones use a 9 month lag in their work (which means 2023 was a La Nina)!


3/ metoffice.gov.uk/research/clima…
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Read 10 tweets
Jun 12
Nitrous Oxide (N2O) is no laughing matter, atmospheric N2O has increased 25% due to human activities.

Today @gcarbonproject updates the Global Nitrous Oxide Budget, which helps us understand where the N2O comes from and where it goes.



1/ essd.copernicus.org/articles/16/25…
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According to IPCC AR6, N2O caused 0.1°C of the current warming of 1.1°C (not this figure is now higher).

This may sound small, but since N2O is long-lived (like CO2) & primarily comes from agriculture, that 0.1°C will only go up in the future.

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There are many sources of N2O, over half of which are natural (soils).

Anthropogenic sources are dominated by agriculture (soils & manure management) & industry (chemicals).

The sink is due to photolysis & oxidation in the atmosphere.

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Read 8 tweets
Jun 5
Greenhouse gas emissions are at record highs, again.

The only good news is that Ozone Depleting Substances (ODS) regulating under the Montreal Protocol have declined substantially in the last decades.

But what does all this mean for climate?



1/ 🧵 essd.copernicus.org/articles/16/26…
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Record high emissions means record high radiative forcing.

We have you covered, we also include aerosols (SO2, etc) & have done so for decades. Also shipping!

Short-lived aerosols are important, but should not distract from the drivers of change: greenhouse gas emissions!

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Most of the energy put into the system ends in the ocean (90%), so the Ocean Heat Content (OHC) has been increasing along with emissions and radiative forcing.

This also means the Earth Energy Imbalance is also increasing.

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Read 8 tweets

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