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  September 7, 2017

Humanity's 'Carbon Budget' is Smaller Than Generally Believed


Professor Michael Mann discusses a new study showing that the IPCC has underestimated global warming in the industrial era
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Humanity's 'Carbon Budget' is Smaller Than Generally BelievedDIMITRI LASCARIS: This is Dimitri Lascaris for The Real News. This is part two of our most recent interview of climate scientist, Professor Michael Mann. Professor Mann is a distinguished research professor and a director of the Earth Systems Science Center at Penn State University. Michael, thank you again for joining us.

MICHAEL MANN: Thanks. Good to be with you.

DIMITRI LASCARIS: Now, at the Paris Climate Conference in 2015, nations of the world agreed to strengthen the United Nations Framework Convention on Climate Change by agreeing to holding the increase in the global average temperature to well below two degrees Celsius above pre-industrial levels, and pursuing efforts to limit the temperature increase to 1.5 degrees Celsius. However, as noted in a study that you recently coauthored, pre-industrial was not defined.

Now, you and some fellow climate scientists have issued this new study called "Importance of the Pre-Industrial Baseline for Likelihood of Exceeding Paris Goals," and it examines the implications of different choices of the pre-industrial baseline, on the likelihood of exceeding the two temperature thresholds set forth in the Paris Climate Accord. Could you tell us, just broadly speaking, about the objective of this study and the methodology you employed in order to achieve that objective?

MICHAEL MANN: Yeah, so I had grown increasingly concerned that we were misidentifying the level of warming that we can tolerate and still consider not being in excess of dangerous levels of warming of the planet. That two degrees Celsius threshold, for warming, relative to pre-industrial time, we're closer [audio drops] you might think based on the way that it's been framed in some past scientific work, and here's the problem. The pre-industrial, meaning before we started burning carbon, burning fossil fuels, and elevating the concentration of C02 and other greenhouse gases in the atmosphere, the industrial revolution began in the late 1700s.

The instrumental record of temperatures that's used to gauge how much the planet is warming only goes back a little more than a century, back to the late 1800s. So, what scientists have typically done is to take the beginning of that record in the late 1800s and for lack of a better definition, used that as an estimate of pre-industrial, and measured the warming that's happened relative to that baseline. Well, the problem is by the time of the late 1800s, we had already burned a lot of carbon. We had already elevated the concentration of greenhouse gases in the atmosphere substantially, and we had already warmed the planet as much as the better part of a half a degree Fahrenheit, several tenths of a degree Celsius.

That means that we are actually closer to exceeding the two degrees Celsius threshold than many scientists had implied in past work, than the IPCC for example, in their last report, the Intergovernmental Panel on Climate Change. They had defined pre-industrial temperatures more or less in that same way, late 1800s, and so we've warmed more than was implied by the last IPCC report. We're closer to that two degree Celsius limit if you use a true estimate of the pre-industrial baseline, and in our study, we used climate model simulations to estimate what temperatures really were during the period before we started burning fossil fuels and elevating the greenhouse effect, going back to the 18th century, the 17th century.

While we don't have widespread thermometer records, we do have simulations that we can use to estimate what temperatures were, and how much warming had happened since then. When you do that, you find that indeed, we're several tenths of a degree Celsius closer to that two degrees Celsius limit. Rather than having warmed only about one degree Celsius, we've probably warmed as much as 1.2-1.3 degrees Celsius relative to the pre-industrial. Here's the problem. We've probably got another half a degree Celsius in the pipeline. Another half a degree Celsius of warming that's going to happen no matter what we do, just from the greenhouse gases we've already put into the atmosphere.

That takes us up to 1.8. Not a whole lot of wiggle room if we're going to avoid two degrees Celsius warming of the planet. And so when we do the calculations, we find that when you take into account this additional warming that had happened before the late 1800s, we probably have as much as 40% less carbon that we can burn. 40% less carbon in our carbon budget, how much carbon we can continue to burn and still remain below two degrees Celsius.

Now, here's the rub. You also referred not just to this two degrees Celsius limit of dangerous interference with the climate, but this aspirational goal that was presented at the last international climate negotiation, this aspirational goal of keeping warming not just below two degrees Celsius, but below 1.5 degrees Celsius because even 1.5 degrees Celsius, less than another half a degree Celsius of warming, will probably, for example, commit many low-lying island nations to inundation. For them, dangerous climate change is closer. It's not two degrees Celsius, it's closer maybe to one and a half degrees Celsius.

Well, what we found in this study is when you use a proper pre-industrial baseline, it's really difficult to see a path towards keeping warming below 1.5 degrees Celsius. If we were to do that, we would probably have to engage in so-called negative emissions. We will actually have to not only transition quickly away from the burning of fossil fuels, but we'll have to pull carbon back out of the atmosphere, using fairly expensive technology.

DIMITRI LASCARIS: I want to talk a little bit about negative emissions. Of course, there's been a big debate about whether we currently have the technological sophistication to achieve negative emissions on a large scale, or a sufficiently large scale. At least one natural tool available to us in order do to that, and that's reforestation. To what degree could reforestation enable us to achieve the necessary level of negative emissions? Is that potentially a powerful tool at our disposal or is that something which inevitability could only play a very small role in sucking C02 out of the atmosphere in order to enable us to avert the worst consequences of climate change?

MICHAEL MANN: Yeah, great question. Frankly, we would be foolish to put all of our eggs in that basket. As you allude to, this is still untested technology. Our ability to deploy a massive sucking machine, as it were, to suck the C02 back out of the atmosphere, at the global scale that would be necessary to make a real dent in the problem, at this point that's theoretical. It's not clear that we could deploy that sort of technology fast enough and at a global scale. Now, in some of the scenarios, for example used in the last IPCC report, some of their scenarios, in particular one scenario with the name, it's called RCP 2.6.

That's technical jargon, but it's basically a scenario that's designed to keep us from warming the planet more than two degrees Celsius with some degree of confidence. Now, in that scenario, they envision a fairly rapid decarbonization of our economy, but they also employ negative emissions later on in the century, and one approach in particular known as BECSS, basically you burn biofuels for energy. So first of all, the energy you're getting is based on carbon that was in the atmosphere previously and all you're doing by burning organic matter is putting it back in the atmosphere. That's where it came from in the first place, so it's sort of a zero sum game.

Even better, if when you burn that carbon, you can capture the C02 and bury it deep below the Earth's surface, then not only is it carbon neutral, you're actually engaging in negative emissions. This would be a way to continue to generate energy and actually engage at the same time in negative emissions. Now, this again, is technology that has not been deployed at nearly the scale that would be necessary really to make a difference. I would argument that rather than banking on our ability to make use of untested technology later in the century, we should simply do what makes more sense, and decarbonize our economy even faster than what's envisioned in the IPCC scenarios.

There is still a scenario for moving forward in keeping within our carbon budget, not warming the planet more than two degrees Celsius, that doesn't require again, banking on theoretical negative emissions technology later in the century, by doing the hard work we need to do now, by simply moving to renewable energy, accelerating the pace of the transition that's already underway from fossil fuels towards renewable energy, doing that even faster, incentivizing that, scaling that up faster. There are credible studies that suggest that we have the technology now to do that.

It's simply a matter of willpower. It's a matter of scaling it up and making that transition as quickly as we can, in part by putting a price on carbon, by leveling the playing field and the energy marketplace so that renewables can compete fairly against fossil fuels. To me, that seems like the logical solution rather than continuing to emit a fairly substantial amount of carbon, under the assumption that we can offset it later in the century. To me, that's kicking the can down the road. It's making a bet, betting with our planet based on something that is not by any measure a sure thing. The more sensible strategy is to just move as quickly as we can to renewable energy.

DIMITRI LASCARIS: I want to talk you about one other aspect of your study. You've indicated that we have to adjust our understanding of the carbon budget based upon a more fact-based assessment of warming that has occurred during the industrial era. When can we expect, on current rates of consumption of fossil fuels, to burn through our actual carbon budget, as you've calculated it with your coauthors in this study?

MICHAEL MANN: Yeah, thanks. If we continue to emit at current levels, which are now roughly about 30 billion tons of carbon dioxide a year, is how much net carbon we're putting into the atmosphere, if we continue at that rate, then you can do the math. We only have a few hundred gigatons, a few hundred billion tons left to burn if we're going to stay within our budget. If we're burning about 30 a year, then it's just a matter of a couple decades until we burn through that budget.

So, clearly it means that we have to bring those emissions down fairly rapidly. Now, here's the good news. The good news is we're already starting to see that bending of the curve. For the last three years, we've seen the global economy increase without any associated increase in carbon emissions. So, that suggests that we are starting to see a separation between economic growth and the burning of carbon. Renewable energy, the deployment of renewable energy policies around the world to incentivize renewable energy, they're already making a difference.

But just keeping those emissions level obviously isn't enough if we're going to avoid burning through the budget. We have to bring those carbon emissions down fairly rapidly. Now, here's the irony. If we had acted in an enlightened manner a couple decades ago when we already knew we had a problem, when the science was already clearly in that we were warming the planet and endangering us by changing our climate. If we had acted in the early 1990s, then that emissions curve, we'd be coming down a bunny slope. We could bring it down fairly gently.

What decades of inaction has bought us now is a trip down a black double diamond slope. We need to bring those emissions down far more dramatically and that's going to require a far greater shock to the system. We're going to have to build new infrastructure, energy infrastructure, far more rapidly. It's going to cost more to act on this problem than it would have if we had acted earlier. That's the problem with deferred maintenance, but here's what would cost far more. Not acting on the problem.

It's clear what the choice is. We need to double down in the actions that are already underway, to move us away from a fossil fuel economy, towards a global clean energy economy.

DIMITRI LASCARIS: In a metaphorical sense, it sounds like we're all going to have to become expert skiers real fast. But I'd like to conclude by asking you about natural cooling and warming trends. Climate change denialists often talk about the natural cooling and warming of the Earth, denying the effect of greenhouse gases from the burning of fossil fuels on our atmosphere. But I understand that in fact, we have been in a naturally cooling period that may have offset some of the climate change that may have otherwise taken place from human activity, and we may be entering a natural heating period. Is that correct? If so, what do you- the implications of that to be?

MICHAEL MANN: Yeah. That's basically right. You sometimes hear this argument from the critics, "Well, how do we know the warming is due to us? Maybe it's due to natural factors." Well, there are thousands of scientists who have spent decades understanding the impact of natural factors on our climate, and we have very reliable estimates now of what those factors are and what impact they've had. It turns out that we've had a large number of explosive volcanic eruptions in recent decades, like the El Chichón eruption in 1982, like the Mount Pinatubo eruption in 1991. Those are natural global cooling effects.

We also know from measurements of solar activity that the sun has been fairly flat, or the output of the sun has even declined slightly in recent decades. That means the natural factors were actually pushing us slightly towards cooling and the warming we've seen actually had to overcome that natural cooling effect. In other words, we are responsible for more than 100% of the warming that we've seen, because we actually overcame a very small but negative trend, a trend in the other direction, from natural factors.

Now, those natural factors vary over time, and the sun, solar output dips during certain time periods, but then it increases over other time periods. Volcanic activity, you tend to see intervals of high activity, followed by intervals of low activity. There's every reason to believe that in the future we are unlikely to see that slight natural cooling trend persist. We're equally likely to see natural factors act in the opposite direction. We're likely to see the opposite side of the coin, and that means that natural factors could in fact add to warming in the decades to come.

The bottom line is that it would be foolish to make policy based on the anticipated impact of natural factors because they work in both directions at different times, and they are so small now compared to the overwhelming impact that we are having by increasing the concentration of greenhouse gases in the atmosphere. We are now firmly in ... We have our hand firmly on the control knob of the climate system, and the focus has to be on us and the carbon that we're burning, and getting away from that behavior so that we don't continue to worsen the problem.

DIMITRI LASCARIS: Well, this has been Dimitri Lascaris speaking to Professor Michael Mann about a new study that has important implications for humanity's carbon budget. Thank you very much for joining us today, Michael.

MICHAEL MANN: Thank you. Always a pleasure.

DIMITRI LASCARIS: And this is Dimitri Lascaris for The Real News.



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