The overwhelming scientific evidence tells us that human greenhouse gas emissions are resulting in climate changes that cannot be explained by natural causes.
Climate change is real, we are causing it, and it is happening right now.
Like it or not, humanity is facing a problem that is unparalleled in its scale and complexity. The magnitude of the problem was given a chilling focus in the most recent report of the International Energy Agency, which their chief economist characterised as the “worst news on emissions.”
It would be easy to form the opinion that everything we know about climate change is based upon the observed rise in global temperatures and observed increase in carbon dioxide emissions since the industrial revolution.
In other words, one could have the mistaken impression that the entirety of climate science is based upon a single correlation study.
In reality, the correlation between global mean temperature and carbon dioxide over the 20th century forms an important, but very small part of the evidence for a human role in climate change.
With many issues to be considered in setting a climate policy one can end up wondering what the role of climate science is in all this.
After all, climate science doesn’t tell us what to do. It doesn’t tell us whether to have a carbon price or where it should be set. Those decisions ultimately involve a range of normative and deliberative issues which are beyond the scope of climatology.
Climatology can tell us, however, what is likely to happen if we don’t act, or if we don’t act with sufficient speed to keep total emissions within specific carbon allocations.
There is no single threshold above which climate change is dangerous and below which it is safe. There is a spectrum of impacts. But some of the largest impacts are effectively irreversible and the thresholds for them are very near.