The skinny on that new IPCC Special Report, in 4 graphs

You’ve probably heard something about the new Special Report, published on October 6, by the International Panel on Climate Change (IPCC).

Links to some popular media articles:

• The Washington Post — The world has just over a decade to get climate change under control, U.N. scientists say
• National Geographic — Climate change impacts worse than expected, global report warns
• The New York Times — Factbox: U.N. report on keeping global warming down to 1.5 degrees Celsius
• The New York Times — Why half a degree of global warming is a big deal
• CNN — Planet has only until 2030 to stem catastrophic climate change, experts warn
• New York Post (later republished by Fox News) — Terrifying climate change warning: 12 years until we’re doomed
• Popular Science — What you should know about the new climate change report
• Motherboard — We’re ‘nowhere near on track’ to meeting our climate change goals, UN report says
• The Economist — Why the IPCC’s report on global warming matters

I’ve spent some time reading the report, which is publicly available here, and this post is to share some of the key takeaways using 4 of the key IPCC graphs.

Though the articles above are largely factually correct, I disagree with the tone of some of them. In particular, I hate the title, “Terrifying climate change warning: 12 years until we’re doomed.” Believing we’re “doomed” is just as paralyzing and irresponsible as denying climate change. It has the effect of externalizing the problem, making it seem like an act of nature or something that’s being done to us. In fact, we are only “doomed” to the extent that we allow ourselves to be.

And, let’s be very clear: insofar as “doomed” means “dispossessed of homes, livelihoods, liberty, and cultural identity by the effects of climate change,” people (including Americans) are already being doomed this very moment. Just read my posts on Shishmaref, Kiribati, Fiji, or indeed Miami. Or, watch the news about the latest hurricane landfall and imagine a future in which those hurricanes intensify decade upon decade. Or take a trip to the Western U.S. during the summer. Or, read about the African “Road of Fire” populated by migrant people fleeing drought, water shortage, crop failures, and resulting violence in their former homes.

The point of the IPCC reports is to rationally describe the challenge and to forecast risks as a result of various policies we might pursue, over which we have control, with the ultimate purpose of defining policies to limit the damage and reduce the future risks.

So, to the IPCC Special Report on Global Warming of 1.5°C:

Who wrote it. There is evidently some question about this among some folks.

“It was given to me. It was given to me, and I want to look at who drew, you know, which group drew it. Because I can give you reports that are fabulous, and I can give you reports that aren’t so good.”

–President of the United States, Donald Trump, approximately 48 hours after the widely expected release of the report commissioned by the 195 nations that are signatories of the Paris Agreement. It’s now 30 days after the report’s release, and I cannot find any evidence the President ever found out “who drew” it, or ever returned to a bouquet of microphones to let us know whether it is “fabulous” or not so good.

It’s actually not a “drawing” per se, but it does contain many informative graphical renderings, two of which we will look at in this post.

In less than 10 minutes of dedicated Googling, I was able to ascertain with a great deal of clarity “who drew” the IPCC Special Report. The report was written by 91 scientists and government agents. Of those lead authors, the greatest number (7) were Americans; the other 84 were from 43 other countries. The lead authors synthesized contributions from 133 contributing authors who drew scientific data and conclusions from over 6,000 cited references in the scientific literature, primarily peer reviewed scientific studies. Drafts of the report were reviewed by some 2,000 registered expert reviewers from 124 countries who generated 42,001 expert review comments that were considered during production of the final report.

To be absolutely clear, there is no “opposing scientific view” on climate change with anything even minutely approaching the credibility of the above detailed effort. The IPCC reports represent, quite literally, the best human understanding of climate change, its predicted consequences, and possibilities for its mitigation.

Why they wrote it. At the time the Paris Agreement was adopted in December, 2015, the 195 nations signing the agreement committed to “holding the increase in the global average temperature to well below 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5°C above pre-industrial levels.” The latter goal was advocated for by the Pacific island nations, which stand to lose the most (which is to say, everything) from even mild levels of global warming compared with our current state. In response to that advocacy, the IPCC was invited to publish, in 2018, a special report on the distinction in global risks between 1.5°C and 2°C of warming, as well as global emission pathways required to achieve one outcome vs. the other. Basically, to answer the question, “Is going through heroics to achieve 1.5°C of warming worth it compared to 2°C of warming? And, if so, is it possible?” This is that report.

What it says, in a nutshell. The report is detailed. It’s 5 chapters and hundreds of pages long. Its key conclusions are very succinctly summarized in a 3-page list of Headline Statements and a 33-page Summary for Policymakers. I highly recommend reading them both. If you’re American, read them before you vote on Nov. 6.

But this is also a case where a picture is worth thousands of words, and so I’d like to reproduce here a couple of the figures the scientists “drew.” If you take nothing else away from the Special Report, sit for a moment with these two images.

First, this one:

The top panel is a graph of global average temperature increase (above the pre-industrial average) vs. year. The grey, squiggly line up to 2017 is the historical measurements (the same data I discuss in detail here). It’s squiggly due to natural variations, which create statistical uncertainty represented by the orange band around the historical data. The orange dashed line is the average projected temperature going forward at the current rate of emissions and global warming, and the horizontal orange error bar represents the statistical uncertainty in the time at which warming will reach 1.5°C. So, we can expect to reach 1.5°C of warming around 2040, but anywhere between 2032 and 2050 accounting for uncertainty. (How old will you be? How about your kids? Your grandkids?)

The purple, grey, and bluish plumes to the right of the top panel are projected global temperature rises based on 3 emission scenarios illustrated in the bottom 3 panels of the figure. The leftmost panel (b) shows annual net CO₂ emissions (amount of CO₂ emitted by fossil fuel use minus amount of CO₂ removed by tree growth, etc.), while the center panel (c) shows net cumulative CO₂ emissions. The rightmost panel (c) shows cumulative “non-CO₂ radiative forcing,” a fancy set of words for emissions of greenhouse gases other than CO₂, such as methane. Starting with the “middle” grey plume of future temperatures, that’s what is expected if we follow the grey emission trajectories in the bottom panels: reduce our global net CO₂ emissions to zero by 2055, in addition to a healthy reduction in other greenhouse gas emissions. If we accomplish the first part, but don’t reduce other greenhouse gas emissions, we get the purple projection. If we are more aggressive, reducing CO₂ emissions to net zero by 2040, as well as accomplishing a healthy reduction in other greenhouse gases, we can achieve the bluish projection.

Thus, it remains possible to ensure we limit warming to 2°C, and it’s even still possible to limit warming to 1.5°C, but either scenario will require dramatic changes in our energy economy over the next 20-35 years.

Here’s a second key graph in the new IPCC report:

These are bars that show scientists’ best consensus forecasts of the severity of impacts and extent of risks in each of a number of categories as a result of allowing the planet to warm various levels above pre-industrial temperatures. The grey band indicates our current level of warming. The risks and impacts get worse as the planet gets warmer (white = “no problem,” purple = “big and irreversible problems”). Anticipating skepticism and in acknowledgement that forecasts are uncertain, the risk colors in the various categories are labeled to indicate their levels of certainty based on available data (M = “medium,” H = “high,” VH = “very high”).

“Even the scientists were surprised to see … how much they could really differentiate and how great are the benefits of limiting global warming at 1.5 compared to 2 [degrees Celsius].”

–Dr. Thelma Krug, IPCC Vice-Chair, in a statement to Reuters

You can easily see in these simple bars the reasoning behind a goal of limiting warming to at most 2°C, or better yet 1.5°C — that’s the range over which key risks and impacts of interest to us (“heat-related morbidity and mortality,” anyone?) are going from “detectable” to “severe and widespread.” Risks in many of these categories are specifically spelled out in simple language in the 3-page Headline Statements, a quick and informative read.

In looking at the graphs above, it’s important to remember the specificity of the question being answered in this latest Special Report. Don’t interpret the “worst” purple plume in the top graph to be “the worst case scenario.” Any of the projections in the above graphs are actually quite good scenarios, which will result from an impressive feat of social and technological success — transforming our economy to reach zero net carbon emissions by mid-century. When we have done that, we will have good reason to be proud!

For a “worst case,” you need to look at similar graphs published in the last full report of the IPCC, the IPCC Fifth Assessment Report (2014):

The above pair of graphs show, on top, annual carbon emissions historically (black) and into the future (various scenarios). The grey scenario is “business as usual,” in which we refuse to admit the problem and just keep on as we have been. The blue scenario is one similar to those considered in the new Special Report: reduction to zero net carbon emissions around mid-century. The bottom graph shows how much warming we expect for each of the given scenarios, which is just a simple result of how much total CO₂ we’ve put into the atmosphere. “Business as usual” — climate change is a “Chinese hoax” and all that — is expected to get us around 4-5°C of warming.

Now, in the graph below, are the same risk bars applied to the broader range of temperature rise we might experience based on our choices starting right now. Lots of reds and purples associated with 4-5°C!

“This report gives policymakers and practitioners the information they need to make decisions that tackle climate change while considering local context and people’s needs. The next few years are probably the most important in our history.”

–Dr. Debra Roberts, Co-Chair of IPCC Working Group II assessing the vulnerability of socio-economic and natural systems to climate change, negative and positive consequences of climate change, and options for adapting to it

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