What can we learn from past warm periods?
With limited political action to control fossil fuel use and associated greenhouse gas emissions, there is increasing emphasis on preparing for inevitable climate changes. But what changes should the world plan for? Model simulations provide some guidance about expected future climate scenarios, but we can also learn from past experience. Although there are no episodes in the past that are strictly comparable to the future, which is a world in which climate is modulated by human activities, there were warm periods in the past which resulted from other forcing factors. There are some lessons we can learn from paleoclimate records about those warm episodes,and the associated environmental changes. This is of particular relevance as we consider future changes in the total amount of snow and ice on the planet, and the consequences for global sea level changes. More than 100 million people currently live within 1m of sea-level, and many major cities are on the coast. With increased population growth and further migration to urban areas, this picture will only become more critical. Added to this concern is the expected increase in extreme weather events, particularly hurricanes and tropical storms, with their associated storm surges along exposed coastlines. Most countries are woefully unprepared for a future with sealevel much higher than today, which will require long-term planning and major investments in protective infrastructures along many coastal regions.