CBC News Technology and Science

Greta Thunberg has talked about a ‘carbon budget.’ [LINK]

What is it, and why does it matter?

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1. THE CBC NEWS REPORT  [LINK]
2. Hello, people! This is our weekly newsletter on all things environmental, where we highlight trends and solutions that are moving us to a more sustainable world.
3. “If we are to have a 67 per cent chance of limiting the global temperature rise to below 1.5 degrees [C], we had, on Jan. 1, 2018, 420 gigatonnes of carbon dioxide left in our CO2 budget. And of course, that number is much lower today. We emit about 42 gigatonnes of CO2 a year. At current emission levels, that remaining budget is gone within 8 1/2 years.” Those words were delivered by youth climate activist Greta Thunberg to the French parliament on July 23, 2019.  She said she has not heard much on the subject of a “carbon budget,” either from politicians or the media. But what’s left in our carbon budget is of utmost importance if we hope to limit global warming.
4. Simply put, this budget refers to how much carbon — which includes CO2 and other greenhouse gases like methane — we can emit into the atmosphere before we pass the point of warming the Earth to 1.5 C or 2 C. The carbon budget was discussed in the first of three special reports by the Intergovernmental Panel on Climate Change (IPCC), released in October 2018. The final installment, the Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC), will be discussed in Morocco this weekend, with a summary due to be released next Wednesday.
5. The Paris Agreement seeks to limit a global temperature rise to 2 C above pre-industrial levels this century (with a goal of keeping it to 1.5 C). The key to understanding the carbon budget is that even if countries keep in line with the Paris accord, if the budget is depleted by then, it won’t matter. The damage will already be done. And it will be irreversible.
6. “If you think about annual emissions and reducing emissions without thinking about the carbon budget, you could really blow past the Paris Agreement,” said Brenda Ekwurzel, director of climate science at the U.S.-based Union of Concerned Scientists. “That’s the trouble.”
7. After a few years of stable global CO2 emissions, they rose in 2018, and there are concerns they may rise again in 2019. If we don’t pay attention to the carbon budget, it increases the chance of a host of global problems: the loss of coral reefs, no summer sea ice in the Arctic, more severe weather events and changes in crops that could lead to further food scarcity. If it sounds dire, Ekwurzel said, but we have the power to change the trajectory.
8. “Whenever we’ve been faced with a problem before and really … lean into it, we make big changes,” Ekwurzel said. “And a lot of those changes we’re calling for, we can do.” She said we need to look at deep de-carbonization of our energy supply, as well as doing “nature-based enhancements,” including the expansion and protection of carbon sinks such as forests, wetlands and mangroves, as well as seagrass. Ekwurzel stresses that economists say the transitions are economically feasible.
9. Like Greta, Ekwurzel said it’s time that everyone — governments, organizations, businesses, and yes, consumers — begin to pay more attention to that budget that is nipping at our heels. She insists that together, we can make a difference. “Yeah,” Ekwurzel said. “We can do this.”
10. RESPONSE TO THE CBC NEWS REPORT
11. The Carbon Budget is constructed with the TCRE [Transient Climate Response to Cumulative Emissions] regression coefficient that expresses the responsiveness of surface temperature to cumulative emissions. The TCRE is a creation of the near perfect correlation between temperature and cumulative emissions discovered by Canadian climate scientist Damon Matthews in his now famous 2009 paper {Matthews, H. Damon, et al. “The proportionality of global warming to cumulative carbon emissions.” Nature 459.7248 (2009): 829}.
12. The TCRE regression coefficient shows that a trillion tonnes of carbon emissions will  cause approximately 1.5C of warming with an uncertainty range of 1C to 2C regardless of how fast, how slow, or what pattern of emission rates generated the amount of cumulative emissions. The versatile and powerful TCRE metric has revolutionized and re-invigorated climate science and rescued it from a  dead end in the climate sensitivity metric imposed by an unmanageable uncertainty problem as described in Knutti 2017 {Knutti, Reto, Maria AA Rugenstein, and Gabriele C. Hegerl. “Beyond equilibrium climate sensitivity.” Nature Geoscience10.10 (2017): 727}.
13. In “Beyond Equilibrium Climate Sensitivity”, Knutti writes {The quest to constrain climate sensitivity has revealed important insights into the timescales of the climate system response, natural variability and limitations in observations and climate models. Estimates of the transient climate response are better constrained by observed warming and are more relevant for predicting warming over the next decades. Newer metrics relating global warming directly to the total emitted CO2 show that in order to keep warming to within 2 °C, future CO2 emissions have to remain strongly limited, irrespective of climate sensitivity being at the high or low end}. The Matthews 2009 and Knutti 2017 papers together are the climate science origin of the climate action metric now known as the carbon budget.
14. And yet, in their excitement for a savior that will rescue them from the climate sensitivity uncertainty dead end and provide them with a tool for climate action in the form of the carbon budget, climate scientists overlooked fundamental issues in statistics that render the TCRE and therefore, the carbon budget as creations of a spurious correlation that have no interpretation in terms of a relationship between emissions and warming that is assumed in climate budgets.
15. These issues are described in related posts at this site listed below.
16. Related Post#1: The spuriousness of correlations between cumulative values of time series data [LINK#1]
17. Related Post#2: The absence of useful information in the carbon budget [LINK#2]
18. Related Post #3 & #4: The Remaining Carbon Budget problem in climate science that demonstrates the futility of the carbon budget concept [LINK#3] [LINK#4]
19. Related Post #5: The statistics of the Remaining Carbon Budget problem in climate science [LINK#5]
20. CONCLUSION: Although the carbon budget appears to be a useful concept in climate science, its utility is illusory because it is based on a spurious correlation that has no interpretation in the real world.

RANDOM NUMBERS WITHOUT SIGN BIAS

RANDOM NUMBERS WITH SIGN BIAS