Symbolic climate milestones 'topple'

3rd August 2016

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  • Ecosystems


Elizabeth Hobday

2015 saw record CO2, temperature and sea levels, according to a major US report. This was partly due to the strong El Niño exacerbating long-term trends.

The annual concentration of CO2 in the atmosphere breached the symbolic milestone of 400 parts per million (ppm) for first time in 2015, according to the US government’s National Oceanic and Atmospheric Administration (NOAA).

The average level seen at the Manua Loa Observatory in Hawaii, the world’s oldest monitoring station, was 400.8ppm. The NOAA says in its annual State of the Climate report that this was ‘a milestone never before surpassed…in measurements of air tapped in ice cores for up to 800,000 years.’

The 2015 level was more than 3ppm higher than in 2014 and the largest increase in the observatory’s 56-year record. The global average concentration was not far below the symbolic milestone either, at 399.4ppm.

The 400ppm level is important because it symbolises that the world is moving closer to dangerous climate change. Scientists have frequently called for CO2 concentrations to be stabilised between 400 and 450ppm if temperature rise is to be kept below 2°C.

The concentration of CO2 was only one of the climate milestones to be toppled in 2015, the report says. Average global surface temperatures were 1°C warmer than pre-industrial levels for the first time, while global average sea levels also hit a new high ­– 70mm higher than in 1993 when satellite monitoring began.

The strong El Niño southern oscillation, present throughout 2015 partly explains why the records were broken so dramatically, the report adds, since it is increases temperatures. It also had dramatic local impacts. In particular, El Niño ‘enhanced precipitation variability around the world’ leading to major floods in Paraguay, Bolivia and Brazil, but equally causing areas defined as in severe drought to expand from 8% to 14%.

The most extreme event exacerbated by El Niño was Indonesia’s annual peat fires. These are started each August to clear lands, but limited precipitation resulted in more widespread and intense fires than usual. By September, much of Indonesia as well as parts of Malaysia, Thailand and Borneo, were covered in thick smoke. The fires led to high levels releases of carbon monoxide and ozone.

‘Last year’s climate was shaped both by long-term change and the El Niño event,’ said NOAA director Thomas Karl. ‘When we think about being climate resilient, both of these time scales are important to consider. The El Niño event was a clear reminder of how short-term events can amplify the relative influence and impacts stemming from longer-term global warming trends.’

The report also reveals that sea ice in the Arctic in 2015 was at its lowest maximum extent since satellite records began almost 40 years ago. It was 7% below average levels between 1981 and 2010. ‘As a consequence of sea ice retreat and warming oceans, vast walrus herds in the Pacific Arctic are hauling out on land rather than on sea ice,’ the report says. This is leading to increased deaths due to overcrowding and is forcing walruses to travel far longer distances for food. Warmer waters are also leading to the expansion of southern fish species, like the Atlantic cod, threatening traditional Arctic species.


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