Making Sense of the Early-2000s Warming Slowdown
It has been claimed that the early-2000s global warming slowdown or hiatus, characterized by a reduced rate of global surface warming, has been overstated, lacks sound scientific basis, or is unsupported by observations.
The evidence presented here contradicts these claims. Climate models did not (on average) reproduce the observed temperature trend over the early twenty-first century, in spite of the continued increase in human-produced greenhouse gases. This mismatch focused attention on a compelling science problem — what is the nature of the naturally-occurring decadal timescale variability in the context of a steady rise of greenhouse gases that produce long term global warming? Our analysis relies on physical understanding of the key processes and forcings involved, in particular the phase of a dominant mode of decadal climate variability called the Interdecadal Pacific Oscillation (IPO).
We find that the rate of warming over the early twenty-first century, when the IPO was in its negative phase, is slower than that of the previous few decades when the IPO was in its negative phase, and these decadal fluctuations are superimposed on a long term multi-decadal warming trend.