2021 is off to a cooler start, with the seventh warmest Jan-April period since records began in the mid-1800s.
That said, it is still warmer than 164 of the 171 years on record, showing just how much human activity has changed what seems normal. carbonbrief.org/state-of-the-c…
Based on the first four months temperatures and the El Nino/La Nina forecast, @CarbonBrief estimates that annual 2021 temperatures also gave the best chance of ending up as the 7th warmest year on record – and its very likely to be somewhere between the fourth and ninth warmest.
We do not expect every year to set a new record in a warming world, as a lot of year-to-year variability is influenced by El Nino and La Nina cycles. The moderate La Nina event in late 2020 and early 2021 is contributing to cooler temperatures, though its is quickly fading:
Observations are still running pretty close to the average projected by all the climate models (CMIP5) included in the last IPCC report:
Sea ice is on the low end of the historical range (1979-2010) in the Arctic, and is close to normal in the Antarctic so far this year:
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Theres been a bit of confusion lately around how the climate system response to carbon dioxide removal. While there are complexities, under realistic assumptions a ton of removal is still equal and opposite in its effects to a ton of emissions.
A thread: 1/x
When we emit a ton of CO2 into the atmosphere, a bit more than half is reabsorbed by the ocean and the biosphere today (though this may change as a warming world weakens carbon sinks). Put simply, 2 tons of CO2 emissions -> 1 ton of atmospheric accumulation.
Carbon removal (CDR) is subject to the same effects; if I remove two tons of CO2 from the atmosphere, the net removal is only one ton due to carbon cycle responses. Otherwise removal would be twice as effective as mitigation, which is not the case.
The carbon cycle has been close to equilibrium through the Holocene; we know this because we measure atmospheric CO2 concentrations in ice cores. But in the past few centuries CO2 has increased by 50%, and is now at the highest level in millions of years due to human emissions.
Starting 250 years ago, we began putting lots of carbon that was buried underground for millions of years into the atmosphere. All in all we’ve emitted nearly 2 trillion tons of CO2 from fossil fuels, which is more than the total mass of the biosphere or all human structures:
About a trillion of that has accumulated in the atmosphere, increasing CO2 concentrations to levels last seen millions of years ago. The remainder was absorbed by the biosphere and oceans. We can measure these sinks, and it’s incontrovertible that they are indeed net carbon sinks
We just published our State of the Climate Q2 update over at @CarbonBrief:
⬆️ Now a ~95% chance 2024 will be the warmest year on record.
⬆️ 13 month streak of records set between June 2023 and June 2024.
⬆️ July 22nd 2024 was the warmest day on record (in absolute terms).
⬇️ July 2024 will very likely come in below July 2023, breaking the record streak.
⬇️ The rest of 2024 is likely to be cooler than 2023 as El Nino fades and La Nina potentially develops.
⬇️ Second lowest Antarctic sea ice on record.carbonbrief.org/state-of-the-c…
The past 13 months have each set a new record, with 2024 being quite a bit warmer than 2023 (at ~1.63C above preindustrial levels) in the ERA5 dataset:
However, the margin by which records are being set has shrunk; global temperatures were setting new records by a stunning 0.3C to 0.5C in the second half of 2023, but have been breaking the prior records (set in 2016, 2020, or 2023) by only 0.1C to 0.2C this year:
Global surface temperatures from @BerkeleyEarth are now out for June. It was the warmest June on record for land, oceans, and the globe as a whole by a sizable margin (~0.14C), and came in at 1.6C above preindustrial levels. berkeleyearth.org/june-2024-temp…
This was the 13th consecutive record setting month, and the 12th month in a row above 1.5C:
The exceptional nature of recent global temperatures really stands out when we look at a 12-month moving average:
Global temperatures were extremely hot in June 2024, at just over 1.5C, beating June 2023's previous record-setting temperatures by 0.14C and coming in around 0.4C warmer than 2016 (the last major El Nino event).
Now 2024 is very likely to beat 2023 as the warmest year on record
June 2024 was so warm that – in the absence of 2023's exceptional warmth – it would have beaten any past July as the warmest absolute monthly temperature experienced by the planet in the historical record:
This plot shows how June 2024 stacked up against all the prior Junes since 1940 in the ERA5 dataset:
We’ve long talked about the carbon budget, but given that the world is on track to pass the 1.5C target in the coming decade its time to start talking about the "carbon debt".
Carbon dioxide accumulates in the atmosphere where it lasts for an extremely long time. While about half of our emissions are removed by land and ocean carbon sinks over the first century, it takes on the order of 400,000 years for nature to fully remove a ton of CO2.
But it turns out that the warming from our CO2 emissions is also extremely long lived. Even if global CO2 emissions ceased and atmospheric CO2 concentrations began to decline, the warming from those emissions would remain for millennia: pnas.org/doi/full/10.10…