Last year, global temperatures were 0.95C warmer than the 20th century average. Human activity is responsible for around 100% of this warming. Delving a little deeper into these figures shows that the Earth's land areas were 1.43C warmer than average, while the oceans were 0.77C warmer. This is evidence of how the world's continents have warmed more rapidly than its oceans over recent decades. This contrast between land and ocean temperature change will strongly shape the global pattern of future warming and has important implications for humans. We are, after all, a species that much prefers to live on land. But what drives this warming contrast? It's a deceptively simple question, but one with a much-misunderstood answer. In this guest post, I outline a robust, quantitative theory for the land-ocean warming contrast that has only been developed in recent years. Simple physics suggests that when you put more heat into the climate system, land should warm more quickly than oceans. This is because land has a smaller 'heat capacity” than water, which means it needs less heat to raise its temperature. The chart below shows how the Earth's land surface (yellow line) has warmed more rapidly than the ocean (dark blue) over the observational record. Amplified warming over land evident in surface temperature records from NOAA. Chart shows annual average temperatures for land (yellow line), ocean (dark blue) and land and ocean combined (light blue). All figures relative to 1901-2000. Data from NOAA; chart by Carbon Brief using Highcharts. This effect can also be seen in different parts of the seasonal climate system. For example, as the sun moves north of the equator during the northern hemisphere spring, its energy rapidly heats India relative to surrounding oceans. This contrast in heating plays a key role in the reversal of winds that drives the South Asia monsoon. Land's small heat capacity also helps to explain... |