Nuggets, facts, figures & definitions

 Could further warming cause the planet's climate systems spiral out of control? In 2019 an international team of scientists published a commentary in the celebrated science journal Nature, sounding the alarm of a planet in crisis — and calling for transformative change.  “We are in a state of planetary emergency,” they wrote, departing from the usual sterility of scientific writing. “The stability and resilience of our planet is in peril.” Yes, they were writing about climate change, but of a particular kind: climate tipping points, elements of the Earth system in which small changes in global temperature can kick off reinforcing loops that ‘tip’ a system into a profoundly different state, accelerating heat waves, permafrost thaw, and coastal flooding — and, in some cases, fueling more warming. The planet has already warmed by roughly 1.2 degrees Celsius (2.2 degrees Fahrenheit) since the Industrial Revolution, and if humans keep flooding the atmosphere with greenhouse gases at the same rate, we’re on track to increase that to 2.7 to 3.1 degrees C (4.9 to 5.6 degrees F) by the end of the century.  So those small changes are getting bigger — increasing the likelihood of triggering those reinforcing loops, known as positive feedbacks. (For example, warming increases the frequency of wildfires, which in turn increases the amount of carbon dioxide released into the atmosphere from burning trees, which leads to an increase in global temperature, which means, you guessed it, even more wildfires.) The scientists identified various elements of the Earth system at risk of reaching points of no return. These elements broadly fall into three categories — ice, sea, and land — and range from the melting of the Greenland ice sheet to the death of coral reefs to the raging of more and more wildfires. The concept of tipping points challenges the dominant understanding of how climate change fundamentally works, says Will Steffen, one of the Nature article’s co-authors and an emeritus professor of climate science at Australian National University. Rather than a dial slowly turning up, tipping elements could compound, he says, combining to build a greater, planetary-wide tipping point. Alternatively, they could push one element out of whack, triggering another to fall out of phase, and then another in a domino-like effect, resulting in a “rapid acceleration of warming until the Earth stabilizes in another state.” These possibilities are far from certain, he admits, but the consequences of a planetary tipping point are severe enough that even a slim risk needs to be taken seriously.  The particular danger, according to the Nature paper’s authors, is that even though the change in a tipping element may happen slowly on a human timescale, once a certain threshold in the system is crossed, it can become unstoppable. This means that even if the planet’s temperature is stabilized, the transition of certain Earth systems from one state to another could pick up speed, like a rollercoaster car that’s already gone over the apex of a track.

https://grist.org/climate-tipping-points-amazon-greenland-boreal-forest/?utm_medium=email&utm_source=newsletter

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The social cost of carbon (SCC) has been called “the most important number you’ve never heard of” because it underpins climate regulations in countries including the US and Canada. It’s one way to put a price on CO2 emissions – but the Trump administration may try to amend it. In this detailed Q&A, Carbon Brief looks at the basics, the science and the politics of the social cost of carbon, as well as the legal situation in the US. You can read all the way through the piece, or jump straight to the section you need with the droplinks, below. Carbon Brief has also produced a timeline, above, showing the key dates in the scientific, regulatory and legal history of the social cost of carbon. You can scroll through the slides using the arrows in the timeline.

  A new analysis found that the social cost of CO2 calculates to at least 15 times the amount that the Biden Administration currently supports, which is $51/ton. The analysis was submitted in a comment to the Office of Management and Budget as part of a process to determine the social cost of greenhouse gases (SC-GHG), which represents a monetary calculation of the cost to society of one additional ton of greenhouse gas emissions.

https://www.carbonbrief.org/qa-social-cost-carbon

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In 2015, by signing up to the Paris Agreement on climate change, nearly every country pledged to keep global temperatures “well below” 2C above pre-industrial levels and to “pursue efforts to limit the temperature increase even further to 1.5C”. Limiting warming to 1.5C requires strictly limiting the total amount of carbon emissions between now and the end of the century. However, there is more than one way to calculate this allowable amount of additional emissions, known as the “carbon budget”.While calculations based on Earth System Models (ESMs, see below) used in the last Intergovernmental Panel on Climate Change (IPCC) report suggest that we have only a few years left at our current rate of emissions before we blow the 1.5C carbon budget, some recent studies have suggested that the remaining carbon budget is much larger.In this article, Carbon Brief assesses nine new carbon budget estimates released by different groups over the past two years. Most show larger allowable emissions than were featured in the last IPCC report. A number of studies suggest that carbon budgets estimates based on ESMs may be on the low side as a result of limitations with how some models represent the carbon cycle. However, there is still a wide range of variation in these new carbon budgets, arising from differences in approaches, timeframes, estimates of warming to-date and other factors. Recent studies suggest the remaining carbon budget to limit warming to “well below” 1.5C might have already been exceeded by emissions to-date, or might be as large as 15 more years of emissions at our current rate. Many new estimates........the idea of a “carbon budget” that ties an amount of future warming to a total amount of CO2 emissions is based on a strong relationship between cumulative emissions and temperatures in climate models. What had started out as a simple communication tool has become quite complicated, with different studies getting very different results as to the allowable carbon budget for very low emission pathways like 1.5C. This relationship between cumulative emissions and warming is not perfect, as it will change based on what happens to non-CO2 greenhouse gases, such as methane and nitrous oxide, as well as how quickly climate-cooling aerosols are reduced. It also does not perform quite as well when there are “net-negative” emissions – when more emissions are being removed from the atmosphere rather than being added.

https://www.carbonbrief.org/analysis-how-much-carbon-budget-is-left-to-limit-global-warming-to-1-5c

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