The Hiatus The Pause The Thing John W. Nielsen-Gammon Regents Professor of Atmospheric Sciences, Texas A&M University Texas State Climatologist

Sen. Cruz vs. Mair, Oct. 8, [5:17 – 6:32]

IPCC AR5 WG1 Explanation of The Thing Natural variability does this sort of thing Radiative forcing was weaker Some models overestimate climate sensitivity Confidence levels: –Medium for explanations –Low for numbers Not discussed: was warming undersampled by observations? [1] [2] [3]

Trends: 0.08 °C/decade to 0.12 °C/decade

Trends: °C/decade, °C/decade, 0.08 °C/decade

Trends: 0.09 °C/decade, 0.07 °C/decade

Total Solar Irradiance

Natural Variability as an Explanation, not an Excuse What natural variations produced a slowdown in warming, and how? Did oceans continue uptake of energy, and how? What does this mean for climate predictions/projections?

ENSO/PDO/IPO: Fun in the Pacific Model with observed East Pacific SST simulates the Thing [1]

ENSO/PDO/IPO: Fun in the Pacific Model with observed East Pacific SST simulates the Thing [4] Same thing happens with observed enhanced trade winds [5] Modeled global temperature can be overly sensitive to tropical Pacific SST [6] Statistical allocation [7] (also [8]): °C anthro, °C Pacific, °C solar

Subsurface Ocean Warming Top 100 m cooled; m layer warmed [9]

Subsurface Ocean Warming Top 100 m cooled; m layer warmed [9] Warm water in West Pacific flows to Indian Ocean [10]

The Thing is Predictable Spin up model with observed winds, and decadal variability can be forecasted [11]

Short-range climate forecasts IPCC AR5 WG1 Fig. 11.9b

Short-range climate verification IPCC AR5 WG1 Fig. 11.9b, updated

IPCC AR5 WG1 Fig a

IPCC AR5 WG1 Fig a, updated

IPCC Model & Expert Judgment IPCC AR5 WG1 Fig b

IPCC Model & Expert Judgment IPCC AR5 WG1 Fig b, updated

Causes of the Thing Natural variability, mainly Pacific Ocean (likely, major) Reduced radiative forcing (solar + ?) (very likely, minor) Observational issues (likely, very minor) Are models overly sensitive? Quite possibly, but not because of The Thing

Contact Information John W. Nielsen-Gammon

References [1] Cowtan and Way, 2014, Quarterly Journal RMS [2] Saffioti et al., 2015, Geophysical Research Letters [3] Karl et al., 2015, Science [4] Kosaka and Xie, 2013, Nature [5] England et al., 2014, Nature Climate Change [6] Douville et al., 2015, Geophysical Research Letters [7] Johansson et al., 2015, Nature Climate Change [8] Dai et al., 2015, Nature Climate Change [9] Nieves et al., 2015, Science [10] Lee et al., 2015, Nature Geoscience [11] Thoma et al., 2015, Geophysical Research Letters

Bonus Slides

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