Source: C. Le Quere and coauthors, Earth Syst. Sci. Data, 10, 2141-2194 (2018)
The increased heat-trapping ability of the additional atmospheric CO2 has alarmed scientists in the past couple of months. They have issued two dramatic calls to action by the nations of the world (here and here) urging humanity to limit the overall rise in the long-term global average temperature to less than 1.5°C (2.7°F) by 2040 or 2050. Voluntary national commitments were made by the members of the United Nations to reduce annual emission rates when the Paris Agreement was reached in 2015. Even at that time, analysis of the commitments recognized that they were seriously insufficient to accomplish the limitation needed. And in the succeeding three years, even those commitments have not been met. This is made worse by President Trump’s intention for the U. S. to leave the Paris Agreement; the U. S. remains one of the three top annual emitters of CO2 in the world and its emissions would increase under the president’s policy.
Global warming depends on the total accumulated greenhouse gases (GHGs), not the annual emissions rate. The heat-trapping effect of GHGs depends on their total accumulated amount in the atmosphere. A goal of simply reducing the annual emission rate does not replace the need to stabilize the total accumulated amount as soon as possible at as low a level as possible. As long as the emission rate is above zero, GHGs continue accumulating in the atmosphere, thereby raising the long-term global average temperature. Only achieving zero GHG emission rates as fast as possible stabilizes the total GHG burden at the low level needed.
This is shown in the model image below. It assumes that we start at a value of 100 for the atmospheric GHG level. From year 0 to year 10 the annual emission rate, shown in blue, is 4% of the amount of the previous year (in the image the rate is multiplied by 25 to scale it to 100). Over this period the cumulative GHG amount, shown in orange, rises by the 4% amount based on the previous year’s level, resulting in a line curving upward:
Historical (black; 1870-2010) and modeled (2010-2100) temperatures (°C) projected for four “scenarios” of differing trends for man-made CO2 concentrations with greatest to essentially no limitations on annual emission rates. Data point dots are given every 10 years. The most stringent (navy blue) falls to a near zero emission rate by 2030-2040; the light blue and orange lines are progressively less stringent, and the red line models the absence of meaningful constraints on emission rates.
Third, bringing annual emission rates to near zero does not reduce the accumulated CO2 level after reaching a plateau, nor does this lower the projected global average temperature. It only keeps the CO2 level and the temperature stabilized.
Many countries in the world are not fulfilling the pledges they made under the Paris Agreement. The New York Times reports, based on the most recent evaluation by the International Energy Agency, that major emitting countries around the world, including China and India, are continuing to build new coal-fired electricity plants instead of migrating to renewable energy on the scale needed. In fact, China and Japan are exporting them, building new coal plants in many developing countries. The United States is reneging on its emissions-reducing policies put in place under former President Obama, and is opening federal lands to new fossil fuel extracting leases. France is showing how difficult the political scene is for pursuing policies to address global warming; rioting citizens are opposing a small, scheduled increase in taxes on vehicle fuels.
This post demonstrates that continuing to emit GHGs at high annual rates inexorably adds to higher CO2 levels in the atmosphere, which leads to higher long-term global average temperatures in a straight-line fashion. Currently there are no technologies ready to be deployed at scale to remove CO2 from emitting facilities or from the air, and permanently to store it away from the atmosphere. Only reducing annual emission rates to near zero in the coming two decades, according to the two reports cited at the outset, (some advocate an even shorter schedule) will keep the world from entering a regime of unacceptably high global average temperatures. All stakeholders need to coalesce around this objective to achieve this goal.
© 2018 Henry Auer