I have definitely reached information overload, which is unfortunate because I am missing Brian Schmidt’s talk. However, of all the things I have heard and seen today, there is one talk I need to write about: Ice cores in Greenland.
Dorthe Dahl-Jensen is one of the most cited scientific authors. period.
That is probably why she can get away with lecturing in this wonderful T shirt.
Dahl-Jensen goes to Greenland with a large team to drill ice cores. And those cores, of course, contain precise records of the climate going back tens and hundreds of thousands of years. From trapped air bubbles, she can tell what the CO2 content of the atmosphere was at any one time. Other isotopes tell her about the ambient temperatures.
And then there is the dust. The dust layers in ancient times were thicker or thinner, and they were blown to Greenland from the loess in China. So a thicker dust layer indicated a dryer period where those soil deposits are in China, and this, in turn, correlates with periods in which the monsoon belt shifted. That is a perfect example of global climate change with local consequences.
Dahl-Jensen doesn’t just look at ice cores, she looks at satellite data that shows that the gravity of Greenland is going down as the ice melting accelerates. She correlates her findings with data from Antarctica and the Hudson delta.
Her findings show that in the past, there has been a sort of see-saw in which the warming in the Northern Hemisphere is accompanied by cooling in the South. But it also shows that there have been periods of abrupt climate change — within 50 years. So some of her research now is looking at whether we could be bringing about this type of abrupt climate change in the future.
The answer, of course, is yes, and she has several scenarios of how this could happen. Funnily enough, she does not think this will occur through the Greenland ice sheet melting. That is because when enough ice has flowed into the ocean through the streams underneath, the sheets will retreat enough that the streams cannot reach the sea. Then there will be more of a stasis between added ice through snowfall and loss though heating.
The big “explosion” will be the breakup of the rest of the Arctic ice. That ice is sitting on a bed that is far below sea level. When the ice sheet loses enough mass through melting, it will just float away, breaking up into smaller pieces that, when they melt, will raise sea levels by meters.
Dahl-Jensen is an optimist, by the way. She loves the science, is aware of the implications, warns us all with a smile, and believes we can adapt. Good luck to us all.