Climate Change Is Likely to Come Sooner and Be Worse Than Latest Worst-Case Forecasts Suggest

The news on climate change has been pretty grim lately, but the fact is, it's possible--even likely--to be far worse than the already sobering news in the latest reports.

Our carbon budgets are likely smaller than we thought, not larger, and the time left before we exceed 1.5degC much shorter than we forecast.

Now, this is going to get a bit wonky, but hang in there--the future viability of the life support system you rely on may be at stake.

First, let's review the headlines from the recent reports, and then examine why warming is likely to be much worse, and come much sooner than even these grim reports suggest.

The recent IPCC report told us that even a temperature increase of 1.5degC could be devastating and that we have very little time to act to avoid it. The Fourth National Assessment told us the U.S. is already experiencing the adverse effects of climate change and that flooding, droughts, fires, and disease would only get worse before it gets better, even if we act immediately.

A recent report in Science conclusively linked the greatest extinction event in geologic history to releases of greenhouse gases from unusually intense volcanic activity--something humans are reproducing at a faster rate today (I wrote about this link back in 2004 in an op-ed for the Baltimore Sun).

Finally, the Global Carbon Project reported that carbon emissions are expected to reach 37.1 billion tons in 2018--an all time high. So as the world gathers to talk about how to implement the Paris agreement at COP 24, we are falling further behind in meeting even its woefully inadequate commitments that will hold warming to 3.5degC, and possibly more.

Pretty scary.

But the bad news is, buried in the IPCC report is an assumption that we actually have a larger carbon budget than we thought, and that means we can emit more carbon than we thought before triggering adverse impacts.

It's very likely that this is flat-out wrong. Here's why.

The explanation for this assumption and why it is dangerously wrong is complicated, but essentially, it's based on the fact that according to historical data, Earth System Models underestimated past emissions by about 280 Gt of CO₂, which means that warming is less responsive to emissions than we thought, and therefore we have a larger carbon budget and more time than we thought (see the carbon brief here for a thorough explanation).

There are several problems with expanding the carbon budget, however. For starters, the carbon budget numbers the IPCC uses in their forecasts assume only a 66 percent chance that the budget will keep us below 1.5degC. In reality, 34 percent of the modeled forecasts using the supposedly acceptable carbon budget numbers result in warming in excess of 1.5degC. This is, as I have said before, a margin of safety we wouldn't accept for a toaster oven, let alone our planet.

But the main problem involves using data from the recent past to forecast the future. When it comes to climate change, the past is not prologue. In fact, in the future, the climate is likely to be more sensitive to a given amount of emissions, not less, because carbon sinks have been compromised. This makes a big difference. For example, the new assumptions in the IPCC report suggest we have about ten years of current emissions remaining before we warm by 1.5degC; under the old ones, we only had three years. But since the sinks are eroding, the expanded carbon budget used in the IPCC's report isn't warranted.

There's ample evidence suggesting that the carbon sinks are getting compromised. For example, there was a great deal of celebration about the fact that human emissions of carbon had flat-lined between 2014 and 2017, but the dirty little secret is that even though emissions held steady, atmospheric concentrations of carbon dioxide continued to go up--indeed, they went up faster than in previous years. In both 2015 and 2016 the atmospheric concentrations went up by 3 parts per million (ppm) which was double the rate of increase between 1990 and 2000.

Many scientists attributed this to the intense El Nino occurring at that time. During El Nino periods, the sinks--natural systems which absorb carbon--are not as effective.

But there is increasing evidence that the sinks are becoming permanently compromised, which means that a higher proportion of the carbon we emit will stay in the atmosphere. In fact, even before the El Nino, research was showing that carbon sinks were becoming less effective at removing carbon from the atmosphere.

The bottom line is that we have no time to act, if we want to have a reasonable chance of avoiding devastating and catastrophic climate change. That's why a Green New Deal is absolutely necessary.

This means that in the future, more of the carbon emitted by humans will remain in the atmosphere--the exact opposite of what the adjusted numbers in the latest IPCC report assume. It also means that even if we do manage to cut carbon emissions in the very near term, we may not have an equivalent cut in atmospheric concentrations, which means warming could continue to go up despite our cuts.

Another factor that is likely to make climate change happen faster than our forecasts suggest is the rapid increase in methane concentrations we've been observing for the last ten years. Methane is about 28 times as strong a greenhouse gas as carbon dioxide over the long term. Isotope data suggests that the bulk of the increase is not due to fossil fuels, and there has been an observed increase in releases of methane from natural sources such as peat, melting permafrost, and clathrates which hold enormous stores of methane.

So, 1) a higher proportion of the carbon we release is likely to stay in the atmosphere, and 2) massive natural stores of methane and carbon are beginning to be released into the atmosphere in addition to the human emissions. This means our carbon budgets are likely smaller than we thought, not larger, and the time left before we exceed 1.5degC much shorter than we forecast.

The bottom line is that we have no time to act, if we want to have a reasonable chance of avoiding devastating and catastrophic climate change. That's why a Green New Deal is absolutely necessary. Nothing short of a World War II-style mobilization will enable us to escape a devastating global meltdown.