Long-term perspective underscores need for stronger near-term policies on climate change

Abstract:

Despite scientific consensus that substantial anthropogenic climate change will occur during the 21^st century and beyond, the social, economic and political will to address this global challenge remains mired in uncertainty and indecisiveness. One contributor to this situation may be that scientific findings are often couched in technical detail focusing on near-term changes and uncertainties and often lack a relatable long-term context. We argue that viewing near-term changes from a long-term perspective provides a clear demonstration that policy decisions made in the next few decades will affect the Earth’s climate, and with it our socio-economic well-being, for the next ten millennia or more. To provide a broader perspective, we present a graphical representation of Earth’s long-term climate history that clearly identifies the connection between near-term policy options and the geological scale of future climate change. This long view is based on a combination of recently developed global proxy temperature reconstructions of the last 20,000 years and model projections of surface temperature for the next 10,000 years. Our synthesis places the 20^th and 21^st centuries, when most emissions are likely to occur, into the context of the last twenty millennia over which time the last Ice Age ended and human civilization developed, and the next ten millennia, over which time the projected impacts will occur. This long-term perspective raises important questions about the most effective adaptation and mitigation policies. For example, although some consider it economically viable to raise seawalls and dikes in response to 21^st century sea level change, such a strategy does not account for the need for continuously building much higher defenses in the 22^nd century and beyond. Likewise, avoiding tipping points in the climate system in the short term does not necessarily imply that such thresholds will not still be crossed in the more distant future as slower components respond. Policies regarding conservation of ecosystems and biodiversity similarly must address contentious issues about the need for environmental triage so that societies invest resources where they are most likely to succeed when faced with an unavoidable trajectory of long-term change.