All the risks of climate change, in a single graph

There are a lot of them.

The risks of climate change are not easy to communicate clearly. Since the atmosphere affects everything, everything will be affected by its warming — there’s no single risk, but a wide and varied array of risks, of different severities and scales, affecting different systems, unfolding on different timelines. It’s difficult to convey to a layperson, at least without droning on and on.

One of the better-known and more controversial attempts to address this problem is a graphic from the reports by the Intergovernmental Panel on Climate Change. The so-called “burning embers” graph attempts to render the various risks of climate change — “reasons for concern,” or RFCs — in an easy-to-grasp visual form.

In a new paper in the journal Nature Climate Change, a group of 17 scholars examines the RFC conceptual framework and reviews the latest science. (Because IPCC reports take so long to produce, the science they contain is always a few years behind.)

Long story short, they find that the graphic is generally accurate (though it has key limitations). They offer suggestions for how the RFC framework could be extended in the future to “better account for possible changes in social and ecological system vulnerability.”

 

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Burning embers: climate risks and when they will kick in

The thermometer on the right shows temperatures relative to preindustrial levels; the thermometer on the left shows them relative to 1986-2005. The distance between the two blue lines is warming that occurred through 2005. (As that note on the right indicates, warming is up a bit 2003-2012.)

Following the IPCC, risks are divided into five buckets or RFCs:

1. Risks to unique and threatened systems. These are ecological or human systems that are geographically constrained and have a high degree of “endemism” — they are uniquely adapted to a particular geography and climate. The authors cite as examples “tropical glacier systems, coral reefs, mangrove ecosystems, biodiversity hotspots, and unique indigenous communities.”
2. Risks associated with extreme weather events. This is what it says, i.e., “risk to human health, livelihoods, assets, and ecosystems from extremes such as heat waves, heavy rain, drought and associated wildfires, and coastal flooding.”
3. Risks associated with the distribution of impacts. This reflects the fact that some groups will be hit earlier and harder than others. Distribution of impacts can be uneven with respect to “geographic location, income and wealth, gender, age, or other physical and socioeconomic characteristics.”
4. Risks associated with global aggregate impacts. This refers to “impacts to socio-ecological systems that can be aggregated globally according to a single metric such as lives affected, monetary damage, number of species at risk of extinction, or degradation and loss of a number of ecosystems at a global scale.”
5. Risks associated with large-scale singular events. These are the much-discussed “tipping points,” whereby a series of incremental changes pushes some system over a threshold, at which point it shifts into a period of rapid, discontinuous, and sometimes irreversible change. The iconic example here is “disintegration of the Greenland and West Antarctic ice sheets leading to a large and rapid sea-level rise.”

Scattered across these five buckets are eight “key risks,” coded by those little colored circles, and which RFC buckets they fall into. Here’s the key to those:

These are the more granular risks: rising sea level, flooding, infrastructure damage, food insecurity, etc.

For each RFC, there are four levels of risk: undetectable, moderate, high, and very high.

The little graphics along the bottom are selected key risks, which are plotted at various points on the graph to illustrate specific dangers. Next to them is a letter indicating the level of confidence scientists feel in predicting the risk — M for medium, H for high.

So, for instance, scientists believe:

• with a high degree of confidence that biodiversity hot spots, coral reefs, and Arctic systems will come under very high risk at 2 degrees;
• with medium confidence that there is high risk of heat waves and extreme precipitation at 2 degrees;
• with medium to high confidence that agriculture is already at moderate risk, which becomes high risk around 2 degrees.

RFCs 4 and 5 are the biggest, scariest dangers — the species-level impacts — but they’re also the ones in which scientists have the least confidence. Still, medium confidence that the Greenland and Antarctic ice sheets will come under high risk by 3 degrees ought to terrify us. That’s gambling with trillions of dollars.

In short, panic

There’s a lot to glean from this graph, but here’s the takeaway: We’ve already crossed over into moderate risk on the first three RFCS. Pushing temperatures up 2 degrees Celsius over preindustrial levels — the target at which the world claims to want to stop warming — puts us at high risk on the first three and moderate risk on the last two. That is the best-case scenario.

Three degrees over preindustrial levels, where we are very likely headed this century, puts us at high risk across the board, very high for those uniquely threatened systems. Five degrees, which is entirely possible, puts basically every human and ecological system at high to very high risk.

We are already in danger, there’s more danger to come, and the best we can hope for is to slow and stop the process before the dangers are catastrophic. That’s the shape of things.

January 9, 2017