Climate Science: My Own Mountain of Evidence

from Wildlife Promise

They should’ve been bound for the recycling bin years ago. So why do I keep dozens of outdated climate reports at my desk here at the National Wildlife Federation?

These climate change assessments — published by the U.N.’s Intergovernmental Panel on Climate Change, various U.S. government agencies, the National Academy of Sciences, and others — are each snapshots of our best understanding of climate change science at the time they were written. They are weighty: dense with text, graphs, tables, and thousands of citations. I keep them because they chronicle the journey that the climate science community has taken over the past generation.

Looking at theses volumes reminds me that the work I do is grounded in an avalanche of evidence – observational data, scientific theory, computer simulations & careful analysis. And it doesn’t stop with these past reports. Every day, more research comes pouring in. It is a full-time job just keeping up with it all.

So when I hear someone claim he’s somehow thrown the world on its head by questioning one aspect of climate science (like the latest brouhaha about emissions from meat production), I think to myself: OK, that’s one page of the thousands here at my desk. Debunking climate science will take a lot more effort than finding a small error here or there.

How much has this body of work grown since the first projections were made? For a flavor of just how much our knowledge has expanded, let’s compare three efforts to assess our best understanding of future warming – dating from 1979, 1995 & 2007:

  • “The Charney Report” (1979). The National Academy of Sciences created a committee of 9 scientists, chaired by pre-eminent MIT atmospheric scientist Jule Charney, to investigate the implications of increasing carbon pollution. The resulting report, Carbon Dioxide & Climate: A Scientific Assessment, is widely cited as being as an impetus for the U.S. Congress, federal agencies, and indeed the international community to take up the issue of climate change. The report authors based their conclusions on a single emissions scenario and five very simple climate models.
    Total pages: 34. Time to prepare: less than 6 months.

  • Climate Change 1995: The Science of Climate Change. This report was the second assessment by the UN Intergovernmental Panel on Climate Change (IPCC). It provided the primary scientific basis for the negotiations leading up to the Kyoto Protocol. The report included climate projections for 6 emissions scenarios and 16 global climate models.
    Total pages: 572. Time to prepare: 13 months.

  • Climate Change 2007: The Physical Science Basis. The UN IPCC’s Fourth Assessment Report is the largest and most detailed summary of climate change science ever undertaken, involving hundreds of authors from dozens of countries. Climate model projections were included for 12 emissions scenarios run on 23 global climate models.
    Total pages: 1056. Time to prepare: more than 3 years.

Each report has brought more information, better understanding of the physical climate system & more confidence in the conclusions. For example, authors of the 1979 Charney Report did not even attempt to determine whether human-caused emissions of carbon dioxide had yet warmed the atmosphere, lacking the data or models sufficiently sophisticated to do so. The 1995 IPCC report concluded that “the balance of evidence suggests a discernible human influence on global climate.”

Just 12 years later, scientific understanding had advanced at an astonishing pace. The 2007 IPCC report stated that “warming of the climate system is unequivocal” and most of the warming since the 1950s is very likely (>90% chance) due to global warming pollution.

Pretty powerful conclusions. And none of the attacks on climate science in the three years since have made even a dent in them.