By James Taylor, 12.05.11, Forbes.com
The central issues in the global warming debate have little to do with whether or not temperatures have warmed during the past century. Nearly all scientists agree that temperatures have indeed warmed during the past 100 years, just as they have warmed (and cooled) many times in previous centuries. The more important issues are whether current temperatures are abnormally warm in a longer-term perspective and whether present warming trends threaten disaster in the foreseeable future.
The first principle to keep in mind is context. While it is true that global temperatures have risen somewhat during the past 100-plus years since the Little Ice Age ended, there was little room for temperatures to go at the time but up. The Little Ice Age, lasting from approximately A.D. 1300 to 1900, brought the planet’s coldest extended temperatures during the last 10,000 years. Saying that temperatures have risen by one degree or so since the end of the Little Ice Age tells us little about the long-term temperature context because the arbitrary baseline of the Little Ice Age was an exceptionally cold climate anomaly.
Keeping this long-term temperature context in mind, we often hear that a given month, year or decade was "the hottest in recorded history," but that statement only holds true when "recorded history" is defined as the past 130 years or so since the depths of the Little Ice Age. Proponents of a global warming crisis justify this convenient definition of "recorded history" based on the establishment of a relatively global system of weather and temperature stations approximately 130 years ago. Fair enough, but proxy climate data from a variety of sources, including ice cores drilled in the Greenland and Antarctic ice sheets, show that global temperatures were warmer for most of the past 10,000 years than they are today. Hu - man civilization first developed, and then thrived, during climate conditions warmer than today. Today’s temperatures, in a more appropriate long-term context, are unusually cold, not hot.
The second principle to remember is that the Earth’s long-term temperature history gives us proof that warmer temperatures have in the real world always been better for human civilization than colder ones. The Little Ice Age was typified by crop failures, famines, plagues, extreme weather events and human population contractions. By contrast, our recently warming temperatures have been a welcome reprieve from the harsh and unusually cold conditions of the Little Ice Age. During the past century as global temperatures have risen, forests have expanded, deserts have retreated, soil moisture has improved, crops have flourished and extreme weather events such as hurricanes and tornadoes have become less frequent.
While our ability to document the frequency of famines, plagues, droughts, hurricanes, etc. is more limited for the millennia before the Little Ice Age, we do know that during these warmer millennia human civilization thrived and the planet’s climate was not thrown into a chaotic downward spiral. Indeed, the Earth’s climate remains quite benign despite these thousands of years of recent warmer temperatures.
This gets to the heart of the global warming debate. If we have real-world evidence that temperatures were warmer during most of the past 10,000 years (and also during several interglacial warm periods over the past few million years) than they are today and if we also have real-world evidence that human civilization thrived during these warmer periods and the warmer temperatures did not trigger so-called "tipping points," sending the planet into a climate catastrophe, then we have little reason to believe our present and moderately warming temperatures are poised to cause a climate catastrophe.
For many scientists this distinction between theory and real-world conditions is what typifies the differences between so-called "alarmists" and "skeptics." As Colorado State University emeritus professor and hurricane expert William Gray frequently explains, alarmists base their climate alarmism on speculative computer models programmed and run within the confines of cubicles and drywall. Skeptics, on the other hand, base their skepticism on real-world data and observations.
Proponents of an imminent global warming crisis may present interesting theories about catastrophes that may occur if the Earth returns to the warmer temperatures that predominated during most of the past 10,000 years, but such theories are strongly contradicted by thousands of years of real-world data and real-world climate observations. The scientific method dictates that realworld observations trump speculative theory, not the other way around.
JAMES TAYLOR IS SENIOR FELLOW FOR ENVIRONMENT POLICY AT THE HEARTLAND INSTITUTE AND MANAGING EDITOR OF ENVIRONMENT & CLIMATE NEWS.