With the data now in for the first half of the year, Carbon Brief estimates that 2020 is most likely to be either the warmest or second warmest year on record, depending on theapproach usedto calculate global temperatures.
在2020年上半年，全球表面温度在2020年上半年具有特别温暖的，与2016年的记录温暖捆绑。这尤其显着，因为El Niñoconditions have been largely “neutral” in 2020 to-date, unlike 2016 which wasconsiderably boostedby an extremely strong El Niño event in the tropical Pacific.
Additionally, June 2020 was the warmest or second warmest June since records began in 1850 across most of the surface temperature datasets analysed by Carbon Brief.
A number of extreme heat events characterised the first six months of 2020;Australia看到记录热量,而西伯利亚经历了staggering heat for much of the first six months of the year – with northern Siberia around 7C warmer than the preindustrial period. This level of extreme heat would have beenalmost impossiblein the absence of human-caused global warming, scientists recently concluded.
Arctic sea ice has also been at record low levels for most of the month of July. While it is too early to know for sure where the summer minimum will end up, 2020 will likely see one of the lowest Arctic sea ice extents on record.
Record heat in first six months
The first six months of 2020 were remarkably warm, either tied with or just a bit behind 2016, currently the record warmest year. Carbon Brief has analysed records from six different research groups that report global surface temperature records:NASA;NOAA;Met Office Hadley Centre/UEA;Berkeley Earth;Cowtan and Way;和Copernicus/ECMWF。
The table below shows the ranking of months – with “1” indicating the warmest temperature on record for that month. Months that were the warmest or tied for the warmest on record are highlighted in green.
|NASA GISTEMP||Hadley/UEA HadCRUT4||NOAA GlobalTemp||Berkeley Earth||牛棚＆方式||Copernicus/ECMWF|
January, April, May and June all had months that set records in at least one of the six datasets.
The figure below shows how temperatures so far in 2020 (red line) compare to prior years (grey lines) in the NASA GISTEMP dataset (using its new版本4.）。It shows the temperature of the year-to-date for each month of the year, from January through to the full annual average.Year-to-date temperatures for each month from 2012 to 2020 fromNASA GISTEMP。关于1981-2010基线绘制的异常。通过碳简短使用图表乐动体育下载appHighcharts。
In the NASA dataset, 2020 ties with 2016 for the warmest January-June average on record. However, 2016 had lower temperatures in the second half of the year, while 2020 has remained quite warm in the past few months. The last 12 months have tied for the warmest 12 months on record in a number of datasets.
The map below shows the distribution of temperatures in the first six months of 2020 across the Earth’s surface. The Siberia region has been strikingly warm so far this year, with many areas 7C warmer than the global average. Europe has also experienced unusual warmth of about 2C above average. Other unusually warm locations include East Asia, Northern Europe and parts of Antarctica.
While human emissions of CO2 and other greenhouse gases areresponsible for all of地球的长期变暖，任何给定年内的温度都受到通常与地球气候的短期变化的强烈影响ElNiño和LaNiña活动。These arefluctuations in temperature在热带太平洋的海洋和大气之间有助于让一些人更加温暖和一些凉爽。
Thefirst half of 2020saw neutral El Niño conditions, likely having little impact on temperatures, thoughthere is evidence在一个温和的LaNiña发展中的过去两个月。预测模型表明，LaNiña的条件将持续到今年下半年，尽管大多数模型只预测到2020年底只有相对较为谦虚的LaNiña事件。
The figure below shows a range of differentEl Niño forecast modelsproduced by different scientific groups. The values shown are sea surface temperature variations in the tropical Pacific – theEl Niño 3.4 region– for three-month periods. Thedynamical modelaverage is shown in red while that for statistical models in shown in green.
全球变暖从厄尔尼诺现象和冷却拉尼娜现象tends to have their maximum impact on global temperatures around three months after conditions peak in the tropical Pacific. This means that even if a strong La Niña develops in the last few months of the year, its main effect would be on temperatures in 2021 rather than 2020.
Good chance 2020 will be warmest year on record
With half the year’s data recorded and forecasts of El Nino development over the next six months now published, it is possible to estimate with reasonable accuracy where 2020 annual temperatures will likely end up.
Carbon Brief has examined the global surface temperature data from all six groups. It has then projected temperatures for the full year of 2020 using the data available to-date for each dataset, along with projection of theEl Niño Indexfor the remainder of 2020 (see methodological note at the end for details).
The results are shown in the figure below. Annual temperatures between 1979 and 2019 are shown in black for each record, while the likely range (95% confidence interval) of the 2020 annual temperature based on the first six months of the year is shown by the red bar.Annual global mean surface temperatures and 2020 estimates fromNASA GISTemp,NOAA GlobalTemp,Hadley/UEA HadCRUT4,Berkeley Earth和Copernicus/ECMWF。关于1981-2010基线绘制的异常。See methodological note below for details. Chart by Carbon Brief usingHighcharts。
For all surface temperature records, 2020 will most likely be either the warmest or second warmest on record. Carbon Brief estimates that two groups – NASA and Copernicus – will very likely have 2020 as the warmest year on record, while the Hadley, Berkeley Earth and NOAA records suggest at this point that it is equally likely to be the warmest or second warmest. Note that Cowtan and Way data was not available through June at the time of publication, and 2020 estimates are not included in these figures.
The probability of where 2020 will fall on the leaderboard of warmest years based temperatures so far this year is shown in the table below.
|NASA GISTEMP||Hadley/UEA HadCRUT4||NOAA GlobalTemp||Berkeley Earth||Cowtan & Way||Copernicus/ECMWF|
There is very little chance that 2020 will not be either the warmest or second warmest year. A lot will depend on what happens to the growing La Nina event in the next three months.
Extreme heat events
The first half of 2020 saw extreme heat events in many parts of the world, with a record settingheatwave in Australiaat the end of 2019 and start of 2020, as well as remarkably persistent high temperatures over Siberia. The figure below shows regions of the world in dark red where the first six months of the year set a record for the warmest first six months since 1850. This includes much of north-central Asia, parts of China, Mexico and South America.
西伯利亚在今年头六个月的大部分时间里都经历了惊人的高温——西伯利亚北部比工业化前时期高出7摄氏度左右。这种程度的酷热almost impossiblein the absence of the long term warming the region has experienced.
The figure below shows temperatures for the first six months of the year for the Siberia region from 1850 through present. The value for 2020 represents a remarkable departure from anything previously seen for the region. It reflects a combination of a long-term, human-caused warming trend – Siberia is one of the fastest warming regions on Earth – and an extremely rare heat event likely due to natural variability.
Warming well in-line with climate models projections
The figure below shows the range of individual models forecasts featured in theIntergovernmental Panel on Climate Change’s(IPCC)第五次评估报告– known collectively as theCMIP5 models- 在1970年和2020年之间，灰色着色和跨越黑色所示的所有模型的平均投影。各个观察温度记录由彩色线表示。
在这些模型中，对2005年以前的气温的估计是利用已知的过去气候影响的“事后预测”，而对2005年以后的气温预测则是基于对情况可能如何变化的估计的“预测”。12-month average global average surface temperatures fromCMIP5 models和observations between 1970 and 2020. Models use RCP4.5 forcings after 2005. They include sea surface temperatures over oceans and surface air temperatures over landto match what is measured by observations。关于1981-2010基线绘制的异常。通过碳简短使用图表乐动体育下载appHighcharts。
While global temperatures were running a bit below the pace of warming projected by climate models between 2005 and 2014, the last few years have been pretty接近模型平均值。This is particularly true forglobally complete temperature records, such as NASA, Berkeley Earth and the Copernicus/ECMWF reanalysis, which include temperature estimates for the whole Arctic. In recent months, temperatures have been a bit above the model average.
Arctic sea ice at record lows
Arctic sea ice spent much of early 2020 at the low end of the historical 1979-2010 range, though over the past few weeks sea ice extent has dropped rapidly, setting new records over the month of July.
Antarctic sea ice was close to the long-term average over the first seven months of 2020. Reliable sea ice coverage data is only available since polar-observing satellites were launched in the late 1970s.
下图显示了2020年北极和南极海冰的范围（红色和蓝色实线）、1979年至2010年的历史范围（阴影区域）和历史低点（黑色虚线）。与全球温度记录不同的是，海冰数据每天都会被收集和更新，使得海冰的范围可以一直观察到现在。Arctic and Antarctic daily sea ice extent from theUS National Snow and Ice Data Center。粗线显示每日2020个值，阴影区域表示two standard deviation rangein historical values between 1979 and 2010. The dotted black lines show the record lows for each pole. Chart by Carbon Brief usingHighcharts。
The summer Arctic sea ice minimum is a somewhat iconic figure and recent years have yet to surpass therecord low set in 2012。While Arctic sea ice is currently at record lows for this time of year, it is unclear if these conditions will persist and it is still too early to know where the 2020 minimum will fall.
The chart below shows the average Arctic sea ice extent for each week of the year for every year between 1978 and 2020, with 2020 to-date highlighted with a thick black line.Arctic and Antarctic weekly sea ice extent from theUS National Snow and Ice Data Centerfrom 1979 through mid-July 2020.
The figure shows a clear and steady decline in Arctic sea ice since the late 1970s, with darker colours (earlier years) at the top and lighter colors (more recent years) much lower. A typical summer now has nearly half as much sea ice in the Arctic as it had in the 1970s and 1980s.
Astatistical multivariate regressionmodel was used to estimate the range of likely 2020 annual temperatures for each group that provides a temperature record. This model used the average temperature over first six months of the year, the latest monthly temperature value (June 2020), the averageENSO 3.4 region valueduring the first six months of the year and the average predicted ENSO 3.4 value during the last six months of the year to estimate the annual temperatures. The model was trained on the relationship between these variables and annual temperatures over the period from 1950 through 2019 (or 1979 through 2019 for theCopernicus/ECMWF reanalysis dataset）。然后，该模型使用这种适合来预测每个组的最可能的2020年度价值，以及95％的置信区间。预测的ENSO 3.4区域值为2020年的2020年的区域值取自NMME model mean forecast。
The percent likelihood of different year ranks for 2020 is estimated by using the output of the regression model, assuming anormal distributionof results. This allows us to estimate what percent of possible 2020 annual values fall above and below the temperatures of prior years for each group.
State of the climate: First half of 2020 sees record heat
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