Zero emissions would quickly stabilise climate

 It had been thought that the lags in climate change were decades long, so that even if we reached zero emissions, global temperatures would keep on rising for decades afterwards.  New research suggests that may not be true. 

From  CleanTechnica

Rising seas, ocean acidification, melting ice caps, raging forest fires, melting tundra — everywhere you look, the news about climate change and the effects of a warming planet is bad. The world’s nations are continuing to spew billions of tons of carbon dioxide and methane into the atmosphere despite all their happy talk about meeting the “spirit” of the accords they signed in Paris in 2015. Is there no respite from the dire news, no relief from the constant drumbeat of bad news and apocalyptic projections?

The conventional wisdom among climate scientists has long been that if we stopped all carbon emissions today, the climate would continue to warm for decades or even centuries. Think of climate change as a really big oil tanker. Even after the engines are shut down, its forward progress continues for miles and miles. That has led many people to throw up their hands in despair and choosing to continue doing what they have always done because if we are doomed, at least let’s have some fun while we still can. It’s like the band playing Nearer My God To Thee on the fantail of the Titanic as it slipped beneath the waves but if the message is that there is no hope, why not?

Writing for Inside Climate News, Bob Berwyn reports on a recent conversation he had with Joeri Rogelj of Imperial College London. Rogelj is not some crackpot on the lunatic fringe of climate science. He is the lead author of the next major climate assessment by the Intergovernmental Panel on Climate Change.

“It is our best understanding that, if we bring down CO2 to net zero, the warming will level off. The climate will stabilize within a decade or two,” Rogelj told Berwyn. “There will be very little to no additional warming. Our best estimate is zero.” He adds the notion that decades or even centuries of additional warming are already baked into the system as suggested by previous IPCC reports was based on an “unfortunate misunderstanding of experiments done with climate models that never assumed zero emissions.”

Those models assumed that concentrations of greenhouse gases in the atmosphere would remain constant and it would take centuries before they decline, Penn State climate scientist Michael Mann told 60 Minutes last October. At the time, Covering Climate Now reported the idea that global warming could stop relatively quickly after emissions go to zero was a “game-changing new scientific understanding.”

Mann told Scott Pelley of 60 Minutes, “This really is true. It’s a dramatic change in the paradigm that has been lost on many who cover this issue, perhaps because it hasn’t been well explained by the scientific community. It’s an important development that is still under-appreciated. It’s definitely the scientific consensus now that warming stabilizes quickly, within 10 years, of emissions going to zero,” he said.

He explained that climate research over the past decade has led scientists to revise their vision of the climate system. Previously, they treated “carbon dioxide in the atmosphere as if it was a simple control knob that you turn up” and temperatures climb accordingly, “but in the real world we now know that’s not what happens.” Instead, if humans “stop emitting carbon right now … the oceans start to take up carbon more rapidly.” The actual lag between halting CO2 emissions and halting temperature rise will not be 25 to 30 years as previously thought but “more like three to five years.”

Global CO2 emissions by sector, 2020.  Source: Statista

This is good news.  Let's suppose we actually manage to cut emissions by 50% by ~2030.  Not impossible: electricity generation and transportation are 57% of total CO2 emissions.  We could switch generation to renewables, and it would pay us to do it, because they're cheaper than coal and gas.  EVs, PHEVs and hybrids could plausibly reach 90% of sales by 2035.  If vehicles have an average life of 15 years, that means by ~2030, at least one third of the vehicle fleet will have an electric motor.  Aircraft and sea transport could use synthetic jetfuel/diesel.  That would increase the emissions reduction to 44%.  Add in green steel, made using green hydrogen instead of coal, and we should be close to a 50% cut (the next 50% will be much harder).

Since the decadal rise in temperature is linearly related to the level of emissions, halving emissions would halve the decadal rise in temperatures from 0.2 degrees C to 0.1 C.  And instead of having to wait 20 or 30 years for this to happen, it will happen in the 40s.  If we halve emissions again in the 40s, the rise in the 50s could be down to 0.05 degrees C.   From then on, we could continue to cut emissions while also starting to remove CO2 from the atmosphere via tree-planting, etc.  This would mean that the total rise in temperatures from now to 2050 would be 0.35 C.  As temps are up roughly 1.2 C since pre-industrial times, that would mean we will have almost limited the rise to 1.5 degrees C.

That's the optimistic outlook.  The pessimistic outlook is that everybody pays lip service to the net-zero 2050 goal, but doesn't do enough to achieve it; fossil fuel interests continue to pervert and subvert politics; and inertia not urgency continue to rule the roost.

How sensitive is the climate to a doubling of CO2?

From ClimateCrocks.

Climate change is real, caused by human activity and a serious problem that needs to be addressed. In a new study published last week, which one of us helped author, we’ve gotten a better understanding of exactly how serious. The good news is that some of the worst-case scenarios seem a bit less likely than before. The bad news is that it’s clearer than ever that warming will not be mild or modest in a world where we fail to cut emissions rapidly.

Climate scientists have been trying to narrow down how, exactly, the climate will respond to increasing levels of carbon dioxide (CO2) for well over a century. We call this “climate sensitivity” — in essence, how sensitive the climate is to our emissions. In 1979 a major report suggested that global surface temperatures would ultimately rise somewhere between 2.7 and 9.1 degrees Fahrenheit (1.5 and 4.5 degrees Celsius) if the amount of CO2 in the atmosphere was doubled. Thirty-five years later, the Intergovernmental Panel on Climate Change gave the same range in their most recent assessment report.

A four-year effort led by 25 experts in the field has finally been able to give us a better understanding of how sensitive the climate actually is. By combining lines of evidence from physics-based studies, historical temperature records and records from the Earth’s more distant past — such as during the last ice age — we find that if the amount of CO2 doubles in the atmosphere, the world will likely warm between 4.7F and 7F (2.6C and 3.9C).  

Such warming may not sound too bad — after all, what difference does a few degrees make? A lot, it turns out. If we go back to the depths of the last ice age, 20,000 years ago, we find that the global average temperature of Earth was only about 9F (5C) colder than today. That was enough of a difference to lower sea level by 300 feet and build up ice sheets thousands of feet thick covering much of North America. That Earth was basically a different planet.  

We now know that a worst-case scenario of high future emissions and high sensitivity risks warming comparable to the warming since the end of the last ice age, occurring over the next one or two centuries. That would impose extremely difficult challenges to human society and natural ecosystems.

It is not inevitable that we will double carbon dioxide in our atmosphere — we control whether we do better or worse than that. We can cut our emissions rapidly enough to avoid doubling CO2 this century, given the political will to do so, and still limit warming below the internationally agreed-upon guardrail value of 3.6F (2C). Alternatively, if our emissions continue increasing, we could end up tripling rather than just doubling atmospheric CO2 by the end of the 21st century. How much warming occurs is up to us, and by narrowing the range of climate sensitivity, we now have a better idea of the consequences of our actions.
On the emissions front we have some reason for modest optimism. Over the past decade, the world has made progress on bending down the emissions curve. Global carbon dioxide emissions are still rising, but only at half the rate they were in the 2000s. [I don't know where they get that from.  See here] The world’s use of coal peaked in 2013 and has been declining. We succeeded in making clean energy less expensive, and carbon-free sources now provide more energy than coal worldwide. Nightmare scenarios where global emissions triple by the end of the century now seem far less likely, as we see them near a plateau.

At the same time, there is an ever-growing gap between where we are today and the emissions reductions needed to limit warming to globally agreed-upon targets. CO2 accumulates in the atmosphere over time, so simply stopping emissions from increasing does not stop the world from warming. Peak emissions — which we will hopefully see this decade — are only the first and easiest step on the long road to zero emissions.

At this point, our findings rule out scenarios where warming ends up being minor, but it also makes some truly catastrophic outcomes less likely. This means that how bad climate change will be rests firmly in our hands. To minimize the risk to future generations, it is crucial to control the one thing we can: our future emissions.

[Dr Zeke Hausfather is the director of climate and energy at the Breakthrough Institute. Dr Andrew Dessler is a professor of Atmospheric Sciences at Texas A&M University.]

    From The Conversation.

At the dawn of the industrial revolution, the Earth’s atmosphere contained 278 parts of CO₂ per million. Today, after more than two and a half centuries of fossil fuel use, that figure is around 414 parts per million (ppm). If the build-up of CO₂ continues at current rates, by 2080 it will have passed 560 ppm – more than double the level of pre-industrial times.


Exactly how the climate will respond to all this extra CO₂ is one of the central questions in climate science. Just how much will the climate actually change?


A major new international assessment of the Earth’s climate sensitivity, now published in the journal Reviews of Geophysics, addresses this question. This research has improved our understanding of how much the world will eventually warm if the carbon dioxide in the atmosphere is maintained at double the level of pre-industrial times.


While an exact figure is still not possible, low levels of warming are now found to be far less likely than previously thought. Very high values are slightly less likely too. There is much greater certainty that, if left unchecked, global warming would be high enough to bring very severe impacts and risks worldwide.


[Sensitivity] can be estimated using three main lines of evidence:

• Temperature measurements made with thermometers from 1850 (when enough global coverage began) to the near present. By comparing temperatures, CO₂ levels and the effect of other climate drivers in the past and present, we can estimate the longer-term changes.
• Evidence from paleoclimate records from the peak of the last ice age 20,000 years ago, when CO₂ was lower than now, and a warm period around 4 million years ago when CO₂ was more comparable to today. We can tell how warm the climate was and how much CO₂ there was in the atmosphere based on the make-up of gases trapped in air bubbles in ancient ice cores.
• Present-day observations – for instance from satellite data – and evidence from climate models, theory and detailed process models that examine the physics of interactions within the climate system.

Global heating assessments for a doubling of CO₂

The ranges estimated in the chart above are wide.  But if you take the centrepoint of the assessments, it is 3 degrees C or more.  This would be catastrophic. We have to stop atmospheric CO₂ doubling.  It's as simple as that.