Indian Ocean key in pause in global warming?


In its 2013 report, the Intergovernmental Panel on Climate Change (IPCC) had reported that the rate of warming was less in the latest 15 years than it was in the previous 30 to 60 years. The apparent pause in global warming might have been a temporary mirage, according to recent NOAA analysis.

Researchers using global data have found that average temperatures have continued to rise throughout the first part of the 21st century. They used data from a correction to ocean-temperature readings, to account for differences in measurements from ships and buoys as well as new land-based monitoring stations that extend into the Arctic — an area where observations are sparse. The updated NOAA dataset also includes observations from 2013 and 2014; the latter ranked as the warmest year on record. The analysis follows a series of papers that sought to explain why global temperatures seemed to level off around the turn of the millennium.

The research has confirmed that there was no true ‘pause’ or ‘hiatus’ in warming.

Climate models used by the IPCC still project warming to continue, but scientists have documented various factors for which the models have not accounted, resulting in suppressed temperatures. These contributors include weak solar irradiation, volcanic aerosols that block sunlight and ocean circulation. (Nature)


Upper ocean may be storing heat, giving atmosphere a break. Scientists have long suspected that oceans have played a crucial role in the so-called warming hiatus by storing heat trapped in the atmosphere by rising levels of greenhouse gases. But pinpointing exactly which ocean acts as a global air conditioner has proved challenging.

The Indian Ocean may explain the puzzling pause in global warming. A study finds that the Indian Ocean may hold more than 70% of all heat absorbed by the upper ocean in the past decade.

Prior research suggested that a significant amount of heat moves from the atmosphere into the Pacific Ocean, where La Niña-like conditions have dominated since the turn of the century.

As a result, wind patterns and ocean currents have increased the drawdown of warm surface waters in the subtropics. This process and others enhance ocean heat uptake. Scientists could not find the extra heat beneath the surface of the Pacific Ocean. In fact the upper 700 metres of the Pacific have actually cooled in recent years.


Using computer models, scientists found that easterly trade winds have strengthened during the hiatus, causing warm water to pile up in the western Pacific. The water seeps between the islands of Indonesia and into the Indian Ocean, through the Makassar Strait bringing heat with it.

In the model, this surge of water produces dramatic warming in the upper Indian Ocean starting in the early 2000s. This explanation also fits with measurements of flow through the Makassar Strait which increased over the same period of time.

Changing patterns of trade winds and ocean currents have stored heat in the Indian Ocean which has been observed. The measurements were for the upper 700 metres of the ocean. However, there is evidence that a significant part of the heat has been going down into the mid and deeper layers which were not accounted for in the study. Other studies have also implicated warming in the North Atlantic and Southern Ocean. The challenge is to understand the energy imbalance of the Earth.