The Two Mile Time Machine

"How do we know what we know about climate change? Richard Alley’s book lays it all out in a very readable an engaging way, from how we can use ice cores – the ‘two mile time machine’ of the title – along with other data sources, not just to document how our climate changed in the past, but why it changed, why it is changing now, and what the future holds. As Alley relates, from isotopic analysis of oxygen in the water molecules that that make up ice cores, along with data from ocean sediment cores and other information, we know that the Earth has experienced a series of ice ages and warm periods (called interglacials). We know that a trigger for going from one to the other is periodic changes in earth orbital geometry called Milankovitch forcings that affect how much solar energy is absorbed by the earth at different latitudes and different time of the year. From analysis of air bubbles trapped in the ice cores, we know that when the climate cooled, carbon dioxide levels in the atmosphere dropped, furthering the cooling. When the Milankovitch effects triggered a warming, carbon than had been stored in the ocean during the cooling phase was released back to the atmosphere, furthering the warming. Ice cores tell also that within these longer-term changes, there were rapid swings in climate linked to adjustments in ocean circulation. In other words, climate and the amount of carbon dioxide in the atmosphere are in lockstep with each other, and big changes in climate can also occur very quickly. “Climate and the amount of carbon dioxide in the atmosphere are in lockstep with each other” A common argument by those who question, or even deny, that humans are changing our climate, falls along the lines of “climate has changed in the past and is always changing through natural processes”. True enough, but what the argument fails to acknowledge is that the physical basis of climate change over the past 150 years is different than anything in the past. Milankovitch forcing is not the answer. Instead, we are taking carbon out of long-term geologic storage, burning it, capturing some of the energy that is released, and then dumping a major combustion product – carbon dioxide – into the atmosphere. The big red flag is that the carbon dioxide level in the atmosphere today is off the charts compared to anything recorded in the ice cores. In climate science, it has been said that a key to understanding the present, and where we are headed, is to understand the past. Nowhere have I seen this articulated in a more compelling way than in The Two Mile Time Machine."