I'm co-author of a recent paper in the journal Oceanography that shows that even if all man-made greenhouse gas emissions were stopped tomorrow and CO2 levels stabilized at today’s concentration, by the end of this century the global average temperature would increase by ~2.4ºC (~4.3ºF) above pre-industrial levels, which is significantly above the level which scientists and policy makers agree is a threshold for dangerous climate change. Of course, greenhouse gas emissions will not stop tomorrow, so the actual temperature increase will likely be significantly larger, resulting in potentially catastrophic impacts to society unless other steps are taken to reduce the Earth’s temperature.
We also find that the United Nation's Intergovernmental Panel on Climate Change (IPCC) 2007 report likely underestimates the potential dangerous impacts that man-made climate change will have on society. Furthermore, while the oceans have slowed the amount of warming we would otherwise have seen for the level of greenhouse gases in the atmosphere, the ocean's thermal inertia will also slow the cooling we experience once we finally reduce our greenhouse gas emissions. This means that the temperature rise we see this century will be largely irreversible for the next thousand years.
The study concludes that because the risks of climate change cannot likely be mitigated solely by reducing greenhouse gas emissions, society should significantly expand research into so-called geoengineering solutions that are meant to either reduce the amount of solar energy that reaches the earth or removes and sequesters greenhouse gases that are already in the atmosphere. Geoengineering solutions must be in addition to, not replace, dramatic greenhouse gas reductions if society is to avoid the most dangerous impacts from climate change.
A few clarifications for those who want to dig in deeper. The +2.4ºC figure refers to an increase above pre-industrial levels and assumes that the atmospheric CO2 concentration stays constant and that aerosol pollution that cools the planet drops out of the atmosphere (after all, we eliminated all CO2 emissions in the scenario). The "danger level" that most scientists and policy makers have agreed to is +2ºC. Note that it is possible that the CO2 concentration may drop if we eliminate CO2 tomorrow (let's hope so). On the other hand, the +2.4ºC figure does not assume "longer term" feedbacks such as methane release from the permafrost or undersea methane hydrates so, on balance, this is probably a best case view and certainly is considering there is no way we are going to eliminate or even drastically reduce CO2 emissions in the next few decades.
On the path we are on, scientists think we will hit +2ºC in 30 or 40 years and +5ºC by the end of the century (and that doesn't include methane release from the permafrost or oceans either!). These temperature numbers don't mean much to most people so I came up with an analogy that might help.
Note that geoengineering includes not only "smoke in the atmosphere" type techniques (albedo management), but also reforestation, biochar, and "artificial trees" (carbon capture and sequestration). And while it is true that some of these techniques (especially the albedo management ones) have bad side effects, like chemotherapy, the alternative is not very acceptable.
We are not calling on governments to implement geoengineering, only to increase research into the techniques. If and when the time comes for deployment (and I think it will come sooner than most people think), we should make decisions based on careful research, not make uninformed decisions out of desperation.
I discuss geoengineering in my FORA.tv talk on climate change. Get a link to the talk here and then you can skip to Chapter 12 once the talks starts (after the ad).