Caldeira Lab

Natural Climate Variability and Future Climate Policy

Katharine Ricke & Ken Caldeira

We know there is a connection between decadal-scale natural climate variability and regional and local extreme weather. We also know that there is a connection between extreme events and perceptions about climate change as a problem. This analysis brings these two ideas together and looks at the implications for national and international climate policies.

Ricke, K. and K Caldeira, Natural Climate Variability and Future Climate Policy, 2014: Nature Clim. Change, 4, 1-6, doi: 10.1038/NCLIMATE2186.

Katharine Ricke - click to read the video transcript




Large ensemble climate modeling experiments demonstrate the large role natural variability plays in local climate on a multi-decadal timescale. Variability in local weather and climate influences individual beliefs about climate change. To the extent that support for climate mitigation policies is determined by citizens' local experiences, natural variability will strongly influence the timescale for implementation of such policies. Under a number of illustrative threshold criteria for both national and international climate action, we show that variability-driven uncertainty about local change, even in the face of a well-constrained estimate of global change, can potentially delay the time to policy implementation by decades. Because several decades of greenhouse gas emissions can have a large impact on long-term climate outcomes, there is substantial risk associated with climate policies driven by consensus among individuals who are strongly influenced by local weather conditions.


Figure 1. Range of time-to-action (in years past 2013) for top six carbon dioxide emitters.  Time-to-action is the time it takes a country to support an international agreement. Box-and-whiskers show the median, 25-75% confidence, and maximum-minimum limits for the 40 ensemble members for each nation/economic entity. Figure 2. Maps of the time-to-action (in years past 2013) by country. Colors indicate the ensemble (a) minimum, (b) median, and (c) maximum for years until 50% of the population of each country has reached the 50%-convinced tipping point for support of international agreement.
Figure 3. Years until an international agreement is reached by world power scheme and policy approach. Histograms of years until: (a) countries representing >50% of world population have agreed to take action, (b) countries representing >50% of world GDP have agreed to take action, (c) China and the US have both agreed to take action. Empty bars illustrate results under the “simultaneous consensus” constraint and light, solid bars show results for the “incremental consensus” constraint. For the ensemble members shown at year 51 in panel c, the criterion for agreement is never met. Figure 4. Years until an international agreement is reached by worldview, power scheme and policy approach. (a) Histogram of the years until an international agreement is reached if citizens weight the experiences of all mankind equally, and (b) box-and-whiskers for all three power schemes and policy processes (colors as in Fig 3) in comparison to the global result (in black).  Arrows illustrate the “ratcheting effect” of an incremental international policy process.