State of the climate: Warm temperatures and low sea ice mark first half of 2017
The first half of 2017 has seen record low sea ice extents at both poles and near-record global average temperatures – despite the absence of a temperature-boosting El Niño event.
In our half-year report, Carbon Brief reviews the state of the climate for 2017 so far and looks ahead at what the rest of the year might bring.
Although it appears unlikely that 2017 will set a record for lowest Arctic sea ice minimum or beat 2016 as the warmest year on record, our analysis suggests that 2017 is set to be the second or third warmest year.
§ On track for one of the warmest years
On the Earth’s surface, global temperatures have been quite warm during the first half of 2017. The first half of the year was the second warmest on record after 2016 in most datasets – even with little effect from El Niño, which was responsible for some of the exceptional warmth in 2015 and 2016. The figure below shows global temperatures from six different scientific groups, along with the year-to-date temperatures in 2017.
NASA GISTemp, NOAA GlobalTemp, Hadley/UEA HadCRUT4, Berkeley Earth, Cowtan and Way, and Copernicus/ERA-Interim. Anomalies plotted with respect to a 1979-2016 baseline. Temperatures only available to the end of May in the Hadley/UEA and Cowtan and Way datasets. Chart by Carbon Brief using Highcharts.In all cases where data is available through to the end of June, temperatures to-date have been lower than those in 2016. However, temperatures are well above where they were prior to 2015, suggesting that unless something changes significantly over the next few months 2017 will be either the second or third warmest year on record.
Temperatures were particularly warm during the first few months of 2017, with a distinct bump in monthly temperatures in February and March in most datasets. This bump appears to be due to high temperatures over the US, Asia and Arctic. Temperatures have fallen in recent months, with June being cooler than any months since mid-2015. The chart below shows monthly temperatures since 2012.
Monthly global mean surface temperatures from NASA GISTemp, NOAA GlobalTemp, Hadley/UEA HadCRUT4, Berkeley Earth, Cowtan and Way, and Copernicus/ERA-Interim. Anomalies plotted with respect to a 1979-2016 baseline. Chart by Carbon Brief using Highcharts.The first six months of 2017 can give a good sense of what to expect for the entire year. By looking at the relationship between the first six months and the annual temperatures for every year since 1950, Carbon Brief has created a projection of what the final global average temperature for 2017 will turn out to be. You can see this in the figure below, which shows the results of our analysis using the NASA GISTemp dataset.
Annual global mean surface temperature anomalies from NASA plotted with respect to a 1979-2016 baseline. To-date 2017 values include January-June. Estimated 2017 annual value based on relationship between January-June mean and annual temperatures since 1950. Chart by Carbon Brief using Highcharts.Here, the yellow dot shows the average 2017 temperature over the first six months, while the red square shows the most likely 2017 annual temperature estimate. The error bars surrounding it indicate the 95% confidence interval – i.e. there’s a 95% likelihood that the 2017 global average temperature will fall in this range.
NASA’s data suggests there is roughly a 10% chance of setting a new record this year, a 73% chance of 2017 being the second warmest year on record, a 17% chance of being the third warmest year, and a less than 1% chance of being fourth or below.
Carbon Brief also carried out a similar analysis for the NOAA dataset, which is similar to the Hadley/UEA HadCRUT4 dataset in that it does not interpolate temperatures outside the regions where it has coverage. This means that it is less sensitive to high Arctic temperatures in recent years and shows 2016 as much less of a record year than in other datasets.
Annual global mean surface temperature anomalies from NOAA plotted with respect to a 1979-2016 baseline. To-date 2017 values include January-June. Estimated 2017 annual value based on relationship between January-June mean and annual temperatures since 1950. Chart by Carbon Brief using Highcharts.Here, our projection suggests 2017 is most likely be the third warmest year on record, with an 8% chance of beating 2016 as the warmest year on record. There’s a 20% chance of being the second warmest, a 72% chance of being the third warmest on record, and a less than 1% chance of being the fourth warmest or below. These numbers are similar to a UK MET Office forecast released in December, which estimated that 2017 would most likely be the third warmest year on record.
Using either the NASA or NOAA data, 2017 will end up as warmer than we’d expect based on the rate of warming since 1970. It will likely end up somewhere close to the average prediction of the latest generation of climate models.
§ Record low sea ice extent at both poles
Global sea ice has been at or near record lows for much of 2017. Both the Arctic and Antarctic have seen some of the lowest sea ice extents over the 1979-2017 satellite record. This year, around 37% of days have seen record low Arctic sea ice and 60% of days have seen record low Antarctic sea ice.
The interactive graph below shows the sea ice extent for both the Arctic (red line) and Antarctic (blue) for every day of the year in 2017 so far, compared to the range of historical values seen during the 1979-2010 period.
US National Snow and Ice Data Center. The bold lines show daily 2017 values, while the shaded area indicates the two standard deviation range in historical values between 1978 and 2010. Chart by Carbon Brief using Highcharts.Here, the shaded area reflects two standard deviations (i.e. ~95% of the observations) around the average sea ice concentration for both the Arctic and Antarctic for the period between 1979 and 2010. Sea ice at both poles has been below the historical range for much of 2017.
Despite low sea ice extent to-date, it appears unlikely that the Arctic will set a new record low at the end of the summer. None of the scientific groups that contribute to the Sea Ice Prediction Network expect 2017 to beat the record set back in 2012 of 3.4m square kilometres (sq km), though most expect it to be lower than last year’s minimum of 4.7m sq km.
While the Arctic minimum set back in 2012 has yet to be surpassed, the long-term trend in the data is clearly downward. The figure below shows Arctic sea ice concentration anomalies (departures from average) for each day since 1978 as blue dots, along with the trend shown in yellow. In the last decade, sea ice has become considerably more variable, with larger dips during the summer melt season followed by recoveries during the winter.
Arctic daily sea ice extent from the US National Snow and Ice Data Center from 1978 to present. Yellow line shows a smoothed (LOWESS) fit to the data to show the long-term trend. Chart by Carbon Brief using Highcharts.The long-term decline in Arctic sea ice is clear and is directly related to rapid warming in the region. While some of the decline and year-to-year variability may be related to natural factors, the impact of warming on the region is relatively clear and future declines in sea ice are expected to continue.
However, it’s worth noting that an ice-free summer is not expected before between 2032 and 2058 – depending on future global greenhouse gas emissions and natural variability.
The changes in sea ice in the Antarctic are much less straightforward. While this year has seen record lows, there is little indication of a long-term trend related to warming – and Antarctic sea ice actually saw record highs as recently as 2014 and 2015. Scientists hoping to solve this puzzle say both natural and human-caused influences could be involved. Antarctic daily sea ice extents are shown in the figure below.
Antarctic daily sea ice extent from the US National Snow and Ice Data Center from 1978 to present. Yellow line shows a smoothed (LOWESS) fit to the data. Chart by Carbon Brief using Highcharts.