The Cause of the Pause

As of 2014, the rate of global mean temperature increase over the 21st century has been less than that over the last quarter of the 20th century. This relative slow-down in global warming is often referred to as ‘the pause’. Below is a compilation of possible explanations for ‘the pause’:

The pause is not surprising given the magnitude of internal variability simulated by models

• Is the climate warming or cooling? – Easterling & Wehner (2009)
• Separating signal and noise in atmospheric temperature changes: The importance of timescale – Santeret al. (2011)
• The role of natural climatic variation in perturbing the observed global mean temperature trend – Hunt (2011)
• Return periods of global climate fluctuations and the pause – Lovejoy (2014)
• Recent global temperature “plateau” in the context of a new proxy reconstruction – Crowley et al., 2014

The pause may be caused by an externally forced energy budget change at the top of the atmosphere

• Stratospheric water vapor
  • Contributions of Stratospheric Water Vapor to Decadal Changes in the Rate of Global Warming – Solomonet al. (2010)
• Anthropogenic Aerosols
  • Reconciling anthropogenic climate change with observed temperature 1998–2008 – Kaufmannet al. (2011)
• Stratospheric aerosols from small volcanoes
  • The Persistently Variable “Background” Stratospheric Aerosol Layer and Global Climate Change – Solomon et al. (2011)
  • Volcanic contribution to decadal changes in tropospheric temperature – Santer et al. (2014)
  • Surface response to stratospheric aerosol changes in a coupled atmosphere–ocean model – Fyfe et al. (2014)
• Solar minimum
• • Earth’s energy imbalance and implications – Hansen et al. (2011)
• CFCs
  • Statistically derived contributions of diverse human influences to twentieth-century temperature changes – Estrada et al. (2013)

The pause may be caused by more energy being transported into the deep ocean

• In the Pacific
  • An imperative for climate change planning: tracking Earth’s global energy – Trenberth (2009)
  • Model-based evidence of deep-ocean heat uptake during surface-temperature hiatus periods – Meehl et al. (2011)
  • Retrospective prediction of the global warming slowdown in the past decade – Guemaset al.(2013)
  • Strengthening of ocean heat uptake efficiency associated with the recent climate hiatus – Watanabe et al. (2013)
  • An Apparent Hiatus in Global Warming? – Trenberth and Fasullo (2013)
  • Recent intensification of wind-driven circulation in the Pacific and the ongoing warming hiatus England et al. (2014)
  • CMIP5 multi-model hindcasts for the mid-1970s shift and early 2000s hiatus and predictions for 2016–2035 – Meehl and Teng (2014)
  • Contribution of natural decadal variability to global warming acceleration and hiatus – Watanabe et al. (2014)
  • Drivers of decadal hiatus periods in the 20th and 21st centuries – Maher et al. (2014)
  • Seasonal aspects of the recent pause in surface warming – Trenberth et al. (2014)
  • Recent observed and simulated warming – Fyfe and Gillett (2014)
• In the Atlantic
  • Varying planetary heat sink led to global-warming slowdown and acceleration – Chen and Tung (2014)

• In the Pacific via the Atlantic
  • Recent Walker Circulation strengthening and Pacific cooling amplified by Atlantic warming – McGregor et al. (2014)

The pause may be caused by El-Niño/La-Niña 

• Global temperature evolution 1979–2010 – Foster and Rahmstorf (2011)
• Recent global-warming hiatus tied to equatorial Pacific surface cooling – Kosaka & Xie (2013)
• Well-estimated global surface warming in climate projections selected for ENSO phase – Risbey et al. (2014)
• The influence of different El Nino types on global average temperature – Banholzer and Donner (2014)
• Natural variability, radiative forcing and climate response in the recent hiatus reconciled – Huber and Knutti (2014)
• Clarifying the Roles of Greenhouse Gases and ENSO in Recent Global Warming through Their Prediction Performance – Triacca et al. (2014)

The pause may be caused by the AMOC/AMO

• Can the Atlantic Ocean drive the observed multidecadal variability in Northern Hemisphere mean temperature? Zhang et al. (2007)
• Advancing decadal-scale climate prediction in the North Atlantic sector – Keenlyside et al. (2008)
• Long-term natural variability and 20th century climate change – Swanson et al. (2009)
• A Significant Component of Unforced Multidecadal Variability in the Recent Acceleration of Global Warming – DelSole et al. (2011)
• On the time-varying trend in global-mean surface temperature – Wu et al. (2011)
• Deducing Multidecadal Anthropogenic Global Warming Trends Using Multiple Regression Analysis – Zhou and Tung (2013)
• Using data to attribute episodes of warming and cooling in instrumental records – Tung and Zhou (2013)
• Decadal variations in the global atmospheric land temperatures – Muller et al. (2013)
• On forced temperature changes, internal variability, and the AMO – Mann et al. (2014)
• Role for Eurasian Arctic shelf sea ice in a secularly varying hemispheric climate signal during the 20th century (2014)
• The Atlantic Multidecadal Oscillation as a dominant factor of oceanic influence on climate (2014)
• Two contrasting views of multidecadal climate variability in the 20th century – Kravtsov et al. (2014)

The Pause may be caused by the North Atlantic Oscillation (through the AMO)

• NAO implicated as a predictor of Northern Hemisphere mean temperature multidecadal variability – Li et al., 2013

The pause is caused by a “climate shift”

• Has the climate recently shifted? – Swanson and Tsonis (2009)

The pause is caused by a persistent Multidecadal Variability Signal

• Application of the Singular Spectrum Analysis Technique to Study the Recent Hiatus on the Global Surface Temperature Record – Macias et al. (2014)

The pause is caused by a confluence of factors

• Overestimated global warming over the past 20 years – Fyfeet al. (2013)
• Reconciling warming trends – Schmidt (2014)
• Natural variability, radiative forcing and climate response in the recent hiatus reconciled – Huber and Knutti (2014)

There is no pause

• Coverage bias in the HadCRUT4 temperature series and its impact on recent temperature trends – Cowtan & Way (2013)
• Global surface temperature change. Hansen et al. (2010)

The pause indicates that climate sensitivity has been over estimated 

• An Objective Bayesian Improved Approach for Applying Optimal Fingerprint Techniques to Estimate Climate Sensitivity – Nic Lewis (2013)

The pause could potentially be caused by unforced changes in the TOA budget (but observations don’t support this)

• Earth’s energy imbalance – Trenberth et al. (2014)
• Internal variability of Earth’s energy budget simulated by CMIP5 climate models – Palmer and McNeall (2014)
• Top-of-atmosphere radiative contribution to unforced decadal global temperature variability in climate models – Brown et al. (2014)

The pause could potentially be caused by an unforced mode in the Southern Ocean

• Southern Ocean Sector Centennial Climate Variability and Recent Decadal Trends – Latif et al. (2013)