Question: so what is warmer climate like?

James Pope answered on 24 Jun 2012:

Hi unclepolly,

A great question and the answer is that it depends on how much warmer the climate is. Firstly, I guess I should explain how we know how the world’s climate was back in the past. For the last 800,000 years we can use ice cores, drilled on Greenland and in Antarctica and perform chemical analysis on gases in the ice and on the ice itself. From 1 million years ago and deeper back in time, we use the shells of plankton. These plankton live for about 2 weeks and they build shells out of minerals in the water, such as calcium (just like your bones!). Those that aren’t eaten by sea life such as whales, die and sink to the bottom of the sea and get buried in the mud. This has been happening for millions of years and so scientists on ships can drill into the sea bed and take cores of the sediment. They then clean off the mud and pick out all the plankton, which we call formainfera. We can study the type of formainfera (as they come in many different species) and we can use chemistry to study their shells and from that we can work out the temperature for the location of that sediment core at different times in the last 80 million years or so. There are a thousend or so of these cores all over the sea bed, but they don’t contain information on every time period, so climate modellers (like me) come along and we can join the dots to try and understand the warmer climates.

I work on a period of time called the Pliocene, this was 3-5 million years ago, and across the whole planet the average temperature was 3°C warmer than the present day, this is an amount of warming that we are very likely to see by 2100 due to climate change.

During the Pliocene, the equator and tropical regions had similar temperatures to the present day, but the polar regions where about 10°C warmer than today. For the UK, we were about 3-5°C warmer than today. This image hopefully shows this, it shows the difference between the Pliocene and today:

This is from some of my model simulations. The images show the difference (which we call ‘anomaly’) between the Pliocene and the Modern day model simulations, which we achieve by doing a subtraction of the Modern from the Pliocene. On the left you can see temperture in degrees Celcius and on the right the change in rainfall from the Pliocene to the modern. These results show that the Pliocene was warmer and slightly wetter than the modern day, and these model results are well supported by the data from formainfera, although the model isn’t exactly right.

But the climate has been very warm over the past 65 million years. 65 million years ago in a period called the Paleocene, it’s just after the dinosaurs have died and the world was on average about 12°C warmer than the present day, there was no ice on Antarctica or Greenland. The world cooled a little bit to about 55 million years ago, when we entered the Eocene, which was 8-10°C warmer, but during the Eocene we had some periods of extreme sudden warming caused by rapid escaping of methane frozen into the sea bed, where there would be an additional 4-8°C of warming over a very short time. This caused a lot of drying out of tropical environments, which was crucial as duing the Paleocene and Eocene it was warm enough to have Aligators inside the Arctic circle, it was that warm up there. During this time the equator may have had temperatures on average of 35-40°C, which is 15°C more than today, so scorchingly hot.

As the world moved from the Eocene to the Oligocene (37 million years ago), we had massive changes to the climate and the world cooled (but was still very much warmer than today). This boundary saw the formation of a very important ocean current, called the Antarctic Circumpolar Current (ACC) when South America and Australia broke away from Antarctica. This caused, climatewise Antarctica to be sealed off from the rest of the world, allowing ice to form on Antarctica for the first time. This cooled the climate to about 6°C warmer than the present day. This slight cooling trend continued through to the Miocene (22-5 million years ago and then we got to the Pliocene.

The image below is in past climate work, famous. It is called the Zachos curve, named after the man who created it, James Zachos, who is an American scientist. He took all the sediment core data for the last 65 million years and plotted it on a single graph.

The graph shows the trends in climate from the death of the dinosaurs (65 million years ago) on the right handside, to the present day on the left.

While the global temperature has changed and cooled through our warmer world to the present day, these changes have happened pver millions of years, even the rapid spikes of warming took tens of thousends of years, we as humans will achieve as big levels of warming but over hundreds of years, just so much faster than nature can, that for me is all the evidence we need that humans are changing out climate.

I hope this is what you were wanting unclepolly, if you want more than just let me know with a comment!

JP