Assigned in the class on climate change I’m auditing at Harvard this semester, this is a deep, scientific look at the mechanisms underlying climate change and the resultant challengers that we are facing.  Archer, a professor of Geophysical Sciences at the University of Chicago, writes clearly and convincingly.  Writing without an obvious political agenda, he presents data from the distant past as the basis for developing models of climate change for our time.  The book is readable, though I wouldn’t recommend it for bed-time browsing.  The take home message for me was that the earth’s climate is the result of many complex factors interacting.  A major influence is the carbon cycle whereby weathering of mountains produces biocarbonate ions that wash to the ocean where they  buffer atmospheric carbon dioxide.  This cycle enables the earth to keep the carbon dioxide concentration in the atmosphere within narrow limits and acts as the earth’s thermostat.  The carbon cycle system operates against the backdrop of variability in the earth’s orbit around the sun (eccentricity, precession, and wobble) which produces a cycle of glaciation and interglacial periods measuring in thousands of years. What characterizes the present time and makes it different from the preceding millions of years is not that we will eventually be ice-free and warmer than at any time since humans evolved, but that the rate of rise of carbon dioxide is so rapid that the buffering capacity of the ocean will take hundreds of thousands of years to be effective.  During that time, the ice sheets will melt, the oceans will rise (perhaps as much as 50 meters, not the 0.5 meters currently predicted) and as many as 10% of the earth’s population will be displaced.  Moreover, Archer points out that there are certain to be unpredictable effects of this unique situation, and those are likely to be feed-forward in nature, worsening the outcomes.  This is not a fear-mongering book but a straight-forward, readable scientific case for why we must alter our ways.  As he points out in the Epilogue, burning one gallon of gas in our car yields about 2500 kilocalories of energy and releases carbon dioxide into the atmosphere. That carbon dioxide acts as a greenhouse gas trapping earth’s radiant energy.  75% of the carbon dioxide will be buffered in the ocean over a few centuries but the rest will remain in the atmosphere for thousands of years and over the course of that time, the gallon of gas will trap one hundred billion kilocalories of useless and unwanted greenhouse heat.  He says, “The bad energy from burning that gallon of gas eventually outweighs the good energy by a factor of 40 million”,  a bad tradeoff.  This is an excellent book for anyone who wants to dive into the science of climate change rather than just read the newspaper headlines.