The PETM and Climate Change Today

The Paleocene-Eocene Thermal Maximum (PETM) is a period in Earth's history that occurred about 55.5 million years ago. The thing that attracts interest to it is how it was a period of global warming. The more scientists study it, the more we are learning about what is happening today. There is good news along with the bad from a recent study. The good news was that the environment adjusted and eventually returned to normal after the global warming episode. While it is good to hear of the adjustment, it is also important to understand the environment took about 200,000 years to fully recover. Left to itself, things will get bad but it won't end the world, But, we may be stuck with this situation for a while.

The PETM is very interesting because of the similarities to today. What has been found is the emission levels were in the ballpark of today's manmade emission levels. The thinking is what happened back then might be a good model for what we can expect to see today. The problem is that it was already much warmer back then when the big emissions came along. In fact, it was so warm there were no ice caps. So it isn't a perfect analogy.

What was seen is the temperature rose by 5 to 8 degrees C (9 to 15 F). That isn't enough to destroy the world, but it sure would cause a lot of devastation. Analysis of sediment cores has indicated there were two pulses of carbon release. It is thought the second one occurred in response to the rising temperature caused by the first. Does that mean we can expect to see something like that today? As the temperature increases due to manmade emissions, can we expect the natural environment to become a CO2 source instead of sink? That would be doubly bad because nature currently removes roughly half of all manmade emissions. If it became a source, it would not only be adding CO2 itself, but would no longer be removing that half of our emissions.

What they have been able to piece together about the PETM is there was a changing climate where some areas became drier and others became stormier. Continent-scale mass migrations have been identified, probably as a result of the changing climate. Some extinctions occurred, but not enough to be a mass-extinction event. The oceans became more acidic.

In other words, pretty much what we are already seeing today. History really does repeat itself for those that don't learn its lesson.

Greenland is Melting Differently

I was reading a report about a presentation at the American Geophysical Union (AGU) meeting in San Francisco last week. Lora Koenig, a glaciologist at the National Snow and Ice Data Center (NSIDC) led a group that found the way ice is melting on the Greenland Ice Sheet changed during the 1990s. The principle means of melting used to be glaciers calving off into the sea. What Koenig's group found is that, while the glacial flow continues, melt ponds have now become the dominant means of mass loss. The ice will melt during the summer and forms bodies of water that range from small ponds to large lakes. This water finds ways to get through the ice and rivers of melt water form. Some of these ponds are even staying liquid through the winter with a layer of insulating snow on top. This provides a jump start on the next melt season. Additionally, the conditions have changed to allow even more melt water to run off. The top layer of snow used to absorb a lot of melt water, but it has now absorbed so much in some places that it is saturated and freezes solid. Since the snow can no longer absorb the melt water, the water flows over the surface and eventually goes into the sea.

So, if the climate isn't changing, as the denier industry wants us to believe, then why is the means of melting changing on something as large as the Greenland Ice Sheet?

Ocean Depths Not Getting Warmer

Scientists at the Jet Propulsion Laboratory have found that the deep oceans below 2000 meters have warmed little, if any, since 2005. This was a very neat study using in situ measurements as well as satellite data. What they did was to measure the increase in total ocean heat content and then subtract what has been measured in the top 2000 meters. What was left over was the amount of warming occurring in the oceans below 2000 meters and they found that it was small, if any.

I am not at all surprised by this result. I know that many people have been saying heat is being stored in the lower levels of the ocean, but my review of the literature did not lead me to that conclusion. There are many reasons, but the fact is that the majority of the deep ocean water originates in the polar areas. As sea water freezes it extrudes the salt, creating a briny soup which is heavier than the surrounding sea water and sinks. Nearly all deep ocean currents originate in the vicinity of Antarctica. For this reason alone, I would have been surprised that the deep ocean was warming. The ocean water around Antarctica is warming, but the briny water will still be nearly freezing because it originates from freezing water. Of course, it is much more complicated than that and there are many other factors involved, but this is the starting point. I just don't see any mechanism to transport heat from the upper-levels to the lower. It all has led me to the conclusion that I was not expecting to find much deep ocean heating.

Now, I know many contrarians are going to point at this study and claim that the oceans are not warming and that is NOT what this study says. What they found is that the DEEP ocean is not warming a perceptible amount. But, note that the only way you can get that result is by finding the upper levels are warming. The way they measured the lower heating is by taking the total heating and subtracting the known amount of upper-level heating. So, this result is only possible with the existence of that upper-level heating.

So, this is a very neat and important study. It does nothing to contradict anything we know about anthropogenic climate change, but it does illustrate we still have lots to learn - and that is not really news.