With Speed and Violence Fred Pearce - Global Commons Institute

There are other disputes, which we might call "second order," because
they are about circumstantial evidence of climate change. Is it true, for
instance, that temperatures at the end of the twentieth century were really
hotter than at any other time in the past millennium? That is the claim made
by U.S. researcher Michael Mann. He produced a controversial graph
dubbed the "hockey stick," which used data from tree rings and other
"proxy" sources to show that the millennium comprised 950 years of stable
temperatures and a sudden upturn at the end. The arguments, which we will
look at in more detail later, continue as to whether Mann's data are correct.
And in the end, we may simply never know enough about past temperatures
to be sure. But however the dispute goes, it doesn't change the basic science
of the greenhouse effect. And in any event, it should be no part of the case for
future climate change that past climate did not vary. It rather obviously did.
As this book will argue, there is no comfort in past variability. Quite the
contrary.
Similarly, there is room for uncertainty about the cause of the rise in
temperature over the past 150 years, which is, depending on how you draw
your average for recent years, put at a global average of between 1. 1 and 1.4 0
F. The warming itself is real enough, but that doesn't necessarily mean that
humans are to blame. It could be natural.
One argument is that more radiation reaching us from the sun can
account for most of the warming of the past 150 years. This case was made
best by the Danish scientists Knud Lassen and Eigil Friis-Christensen in
1991. They found a correlation between sunspot activity, which historically
reflects the energy output of the sun, and temperature changes on Earth
from 1850 onward. Time-based statistical correlations are notoriously tricky,