The recent US election has prompted cries that the decision on Earth’s climate has now been irrevocably made, that the US has unilaterally decided to scrap the peak warming target from the Paris agreement of 1.5 oC. What do the numbers say? Is Earth’s climate now irrevocably fracked?
The short answer is that, strictly speaking, the future of global climate would have been fracked even had the election gone the other way, unless stronger action to cut CO2 emissions is taken, very soon.
Here are some numbers. Carbon emissions from the United States have been dropping since the year 2000, more than on-track to meet a target for the year 2020. Perhaps with continued effort and improving technology, emissions might have dropped to below the 2020 target by 2020, let’s say to 5 gigatons of CO2 per year (5000 megatons in the plot). In actuality, now, let’s say that removing restrictions on energy inefficiency and air pollution could potentially lead to US emissions by 2020 of about 7 gigatons of CO2. This assumes that future growth in emissions followed the faster growth rates from the 1990’s.
Maybe neither of these things will happen exactly, but these scenarios give us a high-end estimate for the difference between the two, which comes to about 4 gigatons of CO2 over four years. There will also probably be extra emissions beyond 2020 due to the lost opportunity to decarbonize and streamline the energy system between now and then. Call it 4-6 gigatons of Trump CO2.
This large quantity of gas can be put into the context of what it will take to avoid the peak warming threshold agreed to in Paris. In order to avoid exceeding a very disruptive warming of 1.5 oC with 66% probability, humanity can release approximately 220 gigatons of CO2 after January, 2017 (IPCC Climate Change 2014 Synthesis report, Table 2.2, corrected for emissions since 2011). The 4-6 Gtons of Trump CO2 will not by itself put the world over this threshold. But global CO2 emission rates are now about 36 gigatons of CO2 per year, giving a time horizon of only about six years of business-as-usual (!) before we cross the line, leaving basically no time for screwing around. To reach the catastrophic 2 oC, about 1000 gigatons of CO2 remain (about 20 years of business as usual). Note that these estimates were done before global temperatures spiked since 2014 — we are currently at 1.2 oC! So these temperature boundaries may be closer than was recently thought.
An optimistic hope is that humanity may soon feel the need to clean up the atmosphere by direct CO2 removal. The American Physical Society estimates a cost for this at about $600 per ton of CO2. Based on this the cost of carbon emitted by the US in the next four years would come in at $8-10 trillion, which amounts to about 14% of US GDP over that time. Even under the scenario that lost in the election, $6 trillion of clean-up costs would have been incurred (8% of GDP).
If you are in a new-found panic about the future of Earth’s climate, know that what you’re feeling now would still have been almost as appropriate had the election gone the other way. The fight to defend Earth’s climate would still be just beginning.