Quote:Why the climate is more sensitive to carbon dioxide than weather records suggest
One of the key questions about climate change is the strength of the greenhouse effect. In scientific terms this is described as “climate sensitivity”. It’s defined as the amount Earth’s average temperature will ultimately rise in response to a doubling of atmospheric carbon dioxide levels.
Climate sensitivity has been hard to pin down accurately. Climate models give a range of 1.5-4.5℃ per doubling of CO₂, whereas historical weather observations suggest a smaller range of 1.5-3.0℃ per doubling of CO₂.
We have seen warming of 1.1°C since pre–industrial times, with CO2 concentrations having increased by over 40%.
Quote:In a new study published in
Science Advances, Cristian Proistosescu and Peter J. Huybers of Harvard University resolve this discrepancy, by showing that the models are likely to be right.
According to their statistical analysis, historical weather observations reveal only a portion of the planet’s full response to rising CO₂ levels. The true climate sensitivity will only become manifest on a time scale of centuries, due to effects that researchers call “slow climate feedbacks”.
Slow climate feedbacks. And oh dear Lees won’t be happy—Bayesian inference
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Quote:slow climate feedbacks, refers to the ultimate consequence of climate response – in other words, the final effects and environmental consequences that a given greenhouse gas concentration will deliver.
These can include long-term climate feedback processes such as ice sheet disintegration with consequent changes in Earth’s surface reflection (albedo), changes to vegetation patterns, and the release of greenhouse gases such as methane from soils, tundra or ocean sediments. These processes can take place on time scales of centuries or more. As such they can only be predicted using climate models based on prehistoric data and paleoclimate evidence.
We know methane is starting to be released from thawing Arctic and Antarctic tundras, but nitrous oxide might be an even bigger cause of these long term climate feedback processes. As sea ice and land based ice sheets melt darker ocean and rocks are exposed. Unlike ice and snow which are white and so reflect a lot of sunlight back into space water and rocks are dark and absorb sunlight and so heat up. This is albedo change. This is why warming is happening twice as fast at the poles as anywhere else on the globe.
Quote:On the other hand, when greenhouse gas forcing rises at a rate as high as 2–3 parts per million (ppm) of CO₂ per year, as is the case during the past decade or so, the rate of slow feedback processes may be accelerated.
Oh
good! So we might get some extra warming from these so–called “slow” longer term feedbacks sooner. Wonderful!
Quote:A study led by climatologist James Hansen concluded that climate sensitivity is about 3℃ for a doubling of CO₂ when considering only short-term feedbacks. However, it’s potentially as high as 6℃ when considering a final equilibrium involving much of the West and East Antarctic ice melting, if and when global greenhouse levels transcend the 500-700ppm CO₂ range.
We are above 400ppm already, allowing for methane we are at about 450ppm CO2 equivalent, not long to go to get to 500ppm and idiots want coal mining and burning to be sped up
And Boobhead thinks, based on a liar’s tales that we are in an ice age.
Quote:Prehistoric climate records for the Holocene (10,000-250 years ago), the end of the last ice age roughly 11,700 years ago, and earlier periods such as the Eemian (around 115,000-130,000 years ago) suggest equilibrium climate sensitivities as high as 7.1-8.7℃.
So far we have experienced about 1.1℃ of average global warming since the Industrial Revolution. Over this time atmospheric CO₂ levels have risen from 280ppm to 410ppm – and the equivalent of more than 450ppm after factoring in the effects of all the other greenhouse gases besides CO₂.
Time for a picture, some peoples’ heads are steaming (assuming they managed to read this far.)
Quote:Climate change is unlikely to proceed in a linear way. Instead, there is a range of potential thresholds, tipping points, and points of no return that can be crossed during either warming or transient short-lived cooling pauses followed by further warming.
The prehistoric records of the cycles between ice ages, namely intervening warmer “interglacial” periods, reveal several such events, such as the big freeze that suddenly took hold about 12,900 years ago, and the abrupt thaw about 8,200 years ago.
In the prehistoric record, sudden freezing events (called “stadial events”) consistently follow peak interglacial temperatures.
Such events could include the collapse of the Atlantic Mid-Ocean Circulation (AMOC), with consequent widespread freezing associated with influx of extensive ice melt from the Greenland and other polar ice sheets. The influx of cold ice-melt water would abort the warm salt-rich AMOC, leading to regional cooling such as is recorded following each temperature peak during previous interglacial periods.
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