2010-19 was the hottest decade on record, finds study as climate crisis worsens globally

As a primary driver for the changing climate, the abundance of many long-lived greenhouse gases continues to increase, reveals analysis

                            2010-19 was the hottest decade on record, finds study as climate crisis worsens globally
(Getty Images)

The last decade was the hottest on record. This is the conclusion reached by 528 scientists representing 61 countries. Each decade since 1980 has been successively warmer than the preceding decade, with the most recent (2010-2019) being around 0.2°C warmer than the previous (2000–2009), write authors. 

2019 was among the three warmest years since records began in the mid-to-late 1800s. According to the experts, only 2016, and for some datasets, 2015 were warmer than 2019. All years after 2013 (that is, from 2014 to 2019) have been warmer than all others back to the mid-1800s, they explain. The report — State of the Climate — was compiled by the National Oceanic and Atmospheric Administration or NOAA’s National Centers for Environmental Information. It highlights the multiple ways in which rising temperatures are changing the planet and human life.

In 2019, there was a record-high number of extreme warm days (temperatures above the 90th percentile) over global land surfaces. There were also a low number of extreme cool days (temperatures below the 10th percentile) compared to the last 70 years, but there were more cool days compared to the average of just the past decade, reveals the study, which has been published in the 30th edition of the Bulletin of the American Meteorological Society. The number of strong marine heatwaves also surpassed the number of more moderate marine heatwaves for the sixth consecutive year.

“The view for 2019 is that climate indicators and observations show that the global climate is continuing to change rapidly. The global average temperature is perhaps the simplest climate indicator through which to view the changes taking place in our climate. 2019 was one of the top three warmest years in the historical record dating back to 1850. It also marks the end of a decade in which the average global temperature had risen by 0.2 °C when compared with the previous decade. And this millennium has been warmer than any comparable period since the Industrial Revolution,” says Robert Dunn from the Met Office. 

The research team found that as a primary driver for the changing climate, the abundance of many long-lived greenhouse gases continues to increase. “A number of extreme events, such as wildfires, heatwaves, and droughts, have at least part of their root linked to the rise in global temperature. And of course, the rise in global temperature is linked to another climate indicator: the ongoing rise in emissions of greenhouse gases, notably carbon dioxide, nitrous oxide, and methane,” explains Dunn.

During last year, the atmospheric concentration of greenhouse gases increased by the following amounts: carbon-dioxide (2.5 parts per million), nitrous-oxide (1 part per billion); and methane (9.2 parts per billion). “The annual global average carbon dioxide concentration at Earth’s surface was 409.8 ± 0.1 ppm, an increase of 2.5 ± 0.1 parts per million (ppm) over 2018, and the highest in the modern instrumental record and in ice core records dating back 800,000 years. Greenhouse gases, along with several halogenated gases, have contributed to a 45% increase in net forcing compared to 1990. Carbon dioxide is responsible for nearly two-thirds of this increase,” write authors.

Many extreme events, such as wildfires, heatwaves, and droughts, have at least part of their root linked to the rise in global temperature, says Robert Dunn from the Met Office (Getty Images)

The warming of the land and ocean surface is reflected across the globe. Lake and permafrost temperatures, for example, have increased, glaciers have continued to lose mass, becoming thinner for the 32nd consecutive year, with the majority also becoming shorter during 2019. For the first time in the observational record at 26 sites in interior Alaska and the Seward Peninsula, the active layer did not freeze completely, a result of long-term permafrost warming and back-to-back relatively mild and snowy winters. The period during which Northern Hemisphere lakes were covered in ice was seven days shorter than the 1981-2010 long-term average, reveals records. Over land, the growing season was an average of eight days longer than the 2000-10 average in the Northern Hemisphere. 

Due in part to precipitation deficits during December 2018-January 2019 — the peak of the rainy season — wildfires scorched vast areas of the southern Amazonian forests in Bolivia, Brazil and Peru, as well as in northern Paraguay, later in 2019. Closer to the equator, 96 named tropical storms were observed during the Northern and Southern Hemisphere storm seasons, well above the 1981-2010 average of 82. 

The continuing warm conditions also influenced water around the globe, with atmospheric water vapor (specific humidity) being high over the ocean surface (one of the moistest years on record), and well above average near the land surface. However, in terms of saturation or relative humidity, the atmosphere was very dry near the land surface, setting a new record low for the global average, and about average over the ocean surface and aloft, the team emphasizes. “Globally, the second half of 2019 saw an increase in the land area experiencing drought to higher, but not record, levels by the end of the year. But annual precipitation amounts were around average, with regional peaks in intense rainfall from, for example, Cyclones Idai and Kenneth in southeastern Africa,” the findings state.

Greenhouse gas levels hit their highest level ever recorded in 2019 (Getty Images)

Among other findings, the study says in 2019, the global mean sea level set a new record for the eighth consecutive year, an increase of 6.1 mm from 2018. Record high ocean heat content measured to 700 meters depth in 2019 contributed an estimated 4.5 mm of that rise. Since 2004, ocean heat content has been increasing at a rate exceeding 0.20°C per decade near the surface and at a lower but still increasing rate of less than 0.03°C decade in deeper waters below 300 meters. The annual globally averaged sea surface temperature was the second-highest on record, surpassed only by the record El Niño year of 2016. “The ocean had a net uptake of about 2.4 billion metric tons of carbon dioxide in 2019. This is a record high amount and an increase of 0.2 billion metric tons from 2018, continuing a trend that began at the start of the twenty-first century,” reveals analysis.

The annual average temperature across land and ocean surfaces “between 20°N and 20°S was +0.47°C above the 1981–2010 average,” making 2019 the third-warmest year for the tropics since records began in 1880, and the warmest since 2016.

The Arctic land surface temperature for 2019 was the second-highest in the 120-year record, following 2016, with record high temperatures in Alaska and northwest Canada. Mean annual Arctic surface air temperatures over land have increased more than twice as fast as the global mean since the mid-1980s. The Antarctic continent also observed its second-warmest year, behind 1980, since the start of the reanalysis record in 1979, at 0.55°C above the 1981-2010 average. The Antarctic ice sheet continued to lose mass, mainly due to interactions between the ocean and the ice sheet, with the highest rates of mass loss occurring in West Antarctica and Wilkes Land, East Antarctica, the researchers explain.

“The last three decades have been pivotal in shifting humanity’s understanding of the impacts of climate change. In 2020, we stand at a mid-point in a climate change journey. We have come a long way in 30 years, but the next 30 years are going to be extremely challenging as we the evidence of climate science and observations to help humanity solve the climate crisis,” writes Albert Klein-Tank, director of the Met Office Hadley Centre.

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