Fifty-six million years ago global temperatures rose several degrees over about 20,000 years (a geological instant).
Corals were nearly wiped out and many planktonic organisms became extinct.
The spike in temperatures marked one of the great upheavals in the Earth's history, known as the Palaeocene-Eocene Thermal Maximum (PETM). Its effects were so dramatic that they are used to mark the boundary between two geological epochs - the Palaeocene and Eocene.
The beginning of the PETM was marked by a massive injection of methane into the atmosphere.
At the low temperatures and high pressures on the ocean floor this gas combines with water to form solid methane hydrate, which is on the seabed in huge amounts - many times more than all the known deposits of coal, oil and natural gas.
Above a critical temperature it breaks down to release methane, a far more powerful greenhouse gas than CO2.
If this were to happen to all the methane hydrate, the quantity of methane released would cause a massive increase in global temperatures.
Many climate scientists think something like that happened at the PETM.
A small rise in global temperature triggered the breakdown of some methane hydrate, causing a further rise in temperature, and the release of more methane, which caused a further rise in temperature, and so on, in a vicious cycle.
This kind of self-accelerating process is called "positive feedback".
Global temperatures are rising far faster than in the PETM, and many climate scientists think we are in great danger of triggering a re-run of the PETM.
James Hansen, the climate scientist who first alerted the world to the dangers of global warming, believes we are in a "planetary emergency" and that unless we take action on a politically unimaginable scale, we are consigning our grandchildren to a ghastly future.
Some data from Nasa may help to make this point.
Every month this year global temperatures have broken records.
January was 1.13C hotter than the baseline for previous Januaries and February was 1.34C hotter than the baseline for previous Februaries.
July was the 10th month in a row that beat all previous global monthly records.
July was not only the hottest July on record, it was the hottest month the world has experienced since records began.
Since 1800, the 10 hottest years have all been after 1997 and the 10 coldest years were all before 1918. Last year was the hottest ever, beating the previous holder, 2014, by a record margin, and scientists predict that there is a 99 per cent chance this year will break the 2015 record.
Why are we so resistant to this knowledge?
Part of the explanation lies in a campaign of disinformation by the fossil fuel companies, particularly the largest, ExxonMobil.
Since the 1980s they consistently maintained that any warming of the climate was entirely natural and not the result of human activity.
But the tide of deception may have begun to change.
Three separate journalistic investigations, by the Columbia Journalism School, Inside Climate News and the Los Angeles Times, have shown that as long ago as 1978, Exxon's senior scientists were telling the management that CO2 emissions would raise global temperatures by 2-3C this century.
Exxon is now under investigation by the Attorneys General of 20 states, in what may prove to be the biggest corporate scandal in American history.
This campaign of lies is chronicled in the book Merchants of Doubt by Naomi Oreskes and Erik Conway.
They show in great detail how the campaign by the fossil fuel companies is but the latest example of how a few politically motivated scientists could ignore overwhelming scientific evidence because of threats to the corporate bottom line by the adverse effects not only of industrial CO2 but also tobacco, acid rain and ozone-depleting chemicals.
All this is very bad news for these merchants of deception, but there is more.
Climate scientists have calculated that to prevent global temperatures from rising above 2C, we cannot afford to burn more that a fifth of the known and accessible fossil fuels.
If the world cannot come to terms with this, a re-run of the PETM is what we may be bequeathing to our children and grandchildren.
True leadership consists in having the courage and integrity to tell the people what they need to hear, rather than what they want to hear.
To slightly mis-quote the American novelist Upton Sinclair: "It is difficult for politicians to understand something if the result of the next election depends on their not understanding it."
No doubt most members of the present Government have children, and many will have grandchildren. In years to come they will have a lot of explaining to do.
Martin Hanson is a retired science teacher based in Nelson.
