What will the Paris climate conference actually accomplish?

This week, 147 heads of state and government, and upwards of 40,000 attendees will gather in Paris at the 21st Conference of Parties to the United Nations Framework Convention on Climate Change (or COP 21) to devise a grand international agreement on climate change, which is supposed to limit global warming to two degrees Celsius.

Amidst all the fanfare and media attention that COP 21 is receiving, there is one very important question—what kind of result will the conference actually produce in terms of limiting global warming?

This is a question which Bjorn Lomborg tried to ask in a recent peer-reviewed journal article that appeared in Global Policy. In the article Lomborg estimated that, based on the Intended Nationally Determined Contributions or INDCs (before the conference, parties had to submit their INDCs explaining how much they plan on reducing their emissions by 2030) of the United States, China, and the European Union, and an estimate for the rest of the world, if emission reduction pledges are met, there will likely be a global reduction of 6.2 to 6.8 gigatonnes of CO2-equivalent emissions by 2030, compared to baseline estimations.

This may sound like a lot but the effect on temperatures is likely to be rather small. Lomborg finds that greenhouse gas emission (GHG) reductions that may result from commitments made for COP 21 in Paris would lead to a year 2100 temperature reduction of 0.17 C in an optimistic scenario, where GHG reductions are at the high end of Lomborg’s estimates; a 0.05 C reduction in the pessimistic scenario, where GHG reductions are at the low end; and an average reduction in temperatures of 0.11 C.

These results are similar to the MIT Joint Program on the Science and Policy of Global Change’s Energy and Climate Outlook 2015 report, which found, regarding the emissions reduction proposals of COP 21, that “[a]ssuming the proposed cuts are extended through 2100 but not deepened further, they result in about 0.2°C less warming by the end of the century compared with our 2014 estimates."

Another question is what will all of these reductions cost?

Again Lomborg sheds some light on this in a recent Wall Street Journal article. After tallying up cost estimates from groups such as the Stanford Energy Modeling Forum and the Asia Modeling exercise, Lomborg found that “the Paris promises of the EU, Mexico, U.S. and China will diminish the economy at least $730 billion a year by 2030.”

That’s a lot of money and prosperity for such a small reduction in temperatures. This is something people should keep in mind throughout the conference in Paris this week.