The Paris Agreement is freely available here, so feel free to peruse it. The summary of key agreements begins at the end of page 21 and continues onto page 22 and includes "holding the increase in the global average temperature to well below 2ºC above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5ºC above preindustrial levels."
A variety of reasons were given by President Trump for the pullout, but I'll focus here on arguments that the Paris Agreement will have little impact on reducing global temperatures. During his speech, President Trump claimed that "even if the Paris Agreement were implemented in full, with total compliance from all nations, it is estimated it would only produce a two-tenths of one degree Celsius reduction in global temperature by the year 2100."
There are two ways one could interpret that statement.
One is that it is patently false. Based on current understanding, holding globally average temperature to 2ºC above preindustrial levels requires emissions reductions, carbon capture and sequestration, and/or other endeavors to limit peak greenhouse gas concentrations to about 450 ppm by about mid century. Under that scenario, global average temperatures stabilize in the latter half of the century (dark blue below, note that the warming on the y-axis is relative to the 1985–2005 average, not preindustrial).
|Source: Secrets of the Greatest Snow on Earth. Adapted from Knutti and Sedláček (2012)|
The other way one might interpret that statement is that President Trump is using something else for the baseline, although I'm not sure what. If that's the case, it was at minimum misleading.
Congressman Chris Stewart of Utah did something a little different. He did some cherry picking.
As summarized in today's Salt Lake Tribune, he "cited predictions that 15 years of compliance by all participating nations would only slow the rise of global temperatures 'by a mere .07 degree Fahrenheit.'"
I don't know what predictions he is referring to specifically, but the key aspect of his statement is that he's focusing on 15 years of compliance, which presumably means the year 2035 since the Paris Agreement enters into force in 2020. In that case, his statement is reasonably accurate, but misleading. Nothing that happens as a result of the Paris agreement is going to have a significant impact on global warming over the next couple of decades. The warming over the next couple of decades is due almost entirely to prior human activity because of the inertia in the climate system and our energy system. No credible scientists dispute this.
However, he's overlooked the fact that the primary impacts of the Paris Agreement occur in the latter half of the 21st century, as clearly indicated by the graph above. The whole point of the Paris Agreement is to manage the risk posed by climate change, including sea level rise, by limiting the total increase in global average temperature. Because of prior greenhouse gas emissions, and the fact that the Earth's climate system is still responding to those emissions, we can't have much of an impact on global warming over the next couple of decades. We can, however, have a major impact in the latter half of the 21st century, and beyond. This is what the Paris Agreement seeks to do.
In general, I am not enamored with International agreements, but what strikes me as significant about Paris is that it is signed by nearly every country and there seems to be tremendous support for it, not only in other countries, but amongst many companies and business leaders. It also is devoid of detail, leaving it to individual countries to set goals and policies (note: this could also be viewed as a weakness).
By pulling out, we've stuck a hot poker in the eye of the International community. On the other hand, progress is being made and participation in the Paris Agreement is not essential for the U.S. to further "bend the curve" on carbon emissions. Just Wednesday, California's Senate passed a bill to receive all of its power from renewable energy by 2045 (it still needs to pass their assembly). Many cities have ongoing plans to reduce greenhouse gas emissions. The migration to clean power in the U.S. continues. Let's do this.