Unsettled: What Climate Science Tells Us, What It Doesn’t, and Why It Matters

by Steven E. Koonin

But another equally serious issue is also illustrated here: Figure 4.3 shows that the ensembles fail to reproduce the strong warming observed from 1910 to 1940. On average, the models give a warming rate over that period of about half what was actually observed. As the IPCC noted in measured and somewhat antiseptic language: It remains difficult to quantify the contribution to this warming from internal variability, natural forcing and anthropogenic forcing, due to forcing and response uncertainties and incomplete observational coverage.13 More bluntly, they’re saying that we’ve no idea what causes this failure of the models. They cannot tell us why the climate changed during those decades. And that’s deeply unsettling, because the observed early twentieth-century warming is comparable to the observed late twentieth-century warming, which the assessment reports attribute with “high confidence” to human influences.