The assumption that current and future climate threats and impacts will resemble those of the past is no longer reliably true.4,27,28 Human-caused carbon pollution in the atmosphere has already pushed many climate-influenced effects—such as the frequency, intensity, or duration of some types of storms and extreme heat, drought, and sea level rise—outside the range of recorded recent natural variability.4,6,28,29 In addition, improved understanding of climate and Earth system science since the advent of systematic data collection in the 19th century has made it clear that the natural variability of the climate system at regional scales is much larger in places than previously understood. For instance, the southwestern United States was much wetter in the 20th century than in most of the preceding thousand years.
The deviation of climate patterns from the recent historical record is expected to grow even larger in the future because of continuing GHG emissions and because the full impact of previous emissions has not yet been felt due to long delays in the climate system’s response to those emissions.3,4,28 Failure to anticipate and adjust to these changes could be costly.
Adjusting to projected climate risk, rather than relying on interpretations of past impacts, has important implications for the location and design of built human infrastructure, engineering standards, insurance rates, property values, land-use plans and planning frameworks or processes, disaster response preparations, and cropland and forest management. In many respects, such climate risk management has attributes familiar to many decision-makers in businesses and communities that commonly manage or design now for a variety of weather-related risks, including storms, heat waves, water availability threats, and floods. Most organizations also manage other short- and longer-term risks and thus have direct experience with preparing for uncertain future conditions over multiple timescales.
However, climate adaptation is also less familiar to some individuals and organizations in that it requires a complete reversal from the near-universal current assumption of an unchanging climate. Many factors make the reversal of this assumption difficult, including unfamiliarity with climate change datasets and concepts; the need to differentiate among the timescales of weather and climate; the challenge of balancing slow-moving, chronic threats and faster, acute ones; the potential and unknown cascading effects of large-scale global changes on local and regional impacts;30 and a lack of public awareness that some current and future changes in climate will be slow to accumulate but will take even longer in time to reverse, for the changes that are reversible.31
The timescales of climate threats also generally do not align with the scales of governance, impeding adaptation progress and often hindering problem identification and solving. Climate change introduces an unfamiliar new source of uncertainty. Where previously an organization may have created plans using a single, well-understood historical record to project a single set of future climate conditions, it now often faces large numbers of climate model projections produced with myriad uncertainties whose local implications may differ significantly across each projection.