Global warming closer to bleak milestone, may move to ‘hothouse’ state not seen in millions of years: Study
Between 2020-2024, the annual mean global near-surface temperature is predicted to be between 0.91°C and 1.59°C above pre-industrial conditions, defined as the 1850-1900 average, says the UN report
The world is set to see its warmest five years on record – in a trend which is likely to continue – and is not on track to meet agreed targets to keep global temperature increase well below 2°C or at 1.5°C above pre-industrial levels, according to scientists. They warn that the world is inching closer to crossing the temperature limit of 1.5°C set five years ago in the Paris Agreement.
Between 2020-2024, the annual mean global near-surface temperature is predicted to be between 0.91°C and 1.59°C above pre-industrial conditions, defined as the 1850-1900 average, says the United Nations (UN) report. During these five years, the chance of at least one year exceeding 1.5°C above pre-industrial levels is 24%, with a very small chance (3%) of the five-year mean exceeding this level. It is likely (about 70% chance) that one or more months during the next five years will be at least 1.5°C warmer than pre-industrial levels. “There is a growing chance of annual global mean near-surface temperature temporarily exceeding 1.5°C above the 1850-1900 pre-industrial level, in the five-year period ending in 2024. There is a high risk of unusual regional rainfall over the period, with some regions experiencing increasing drought-related risks and others increased risks associated with heavy rainfall,” write authors.
According to the analysis, the average global mean surface temperature for 2016-2020 (2020 data are based on averages January to July) will be among the warmest of any equivalent period on record. “It is currently estimated to be 1.1°C (±0.1°C) above pre-industrial (1850–1900) times and 0.24°C (±0.10°C) warmer than the global mean surface temperature for 2011-2015. The 2016-2020 five-year average temperatures are on course to be the highest on record for much of Europe, the Middle East and northern Asia, southern and eastern areas of the US, areas of South America, southern Africa, and Australia. Over 2020–2024, many parts of South America, southern Africa, and Australia are likely to be dryer than the recent past,” the findings state.
Coordinated by the World Meteorological Organization (WMO), the findings show that the levels of atmospheric carbon dioxide, methane, and nitrous oxide are rising. Benchmark stations in the WMO Global Atmosphere Watch (GAW) network reported carbon dioxide concentrations above 410 parts per million (ppm) during the first half of 2020, with Mauna Loa (Hawaii) and Cape Grim (Tasmania) at 414.38 ppm and 410.04 ppm, respectively, in July 2020, up from 411.74 ppm and 407.83 ppm in July 2019. Reductions in emissions of carbon dioxide in 2020 as a result of lockdowns due to the Covid-19 pandemic, will only slightly impact the rate of increase in the atmospheric concentrations, which are the result of past and current emissions, as well as the very long lifetime of carbon dioxide, say experts. They add that sustained reductions in emissions to net-zero are necessary to stabilize climate change.
While global greenhouse gas emissions have continued to increase, the emissions gap is also larger than ever. Even with full implementation of the current Nationally Determined Contributions (NDCs), the emissions gap in 2030 will be around 15 gigatonnes of carbon dioxide equivalent for a 2°C goal, and 32 gigatonnes of carbon dioxide equivalent for a 1.5°C goal. The current level of climate ambition sets the world on course to a global average temperature increase of 3.0 to 3.2°C by the end of this century.
The research team cautions that transformational action can no longer be postponed if the Paris Agreement targets are to be met. “The Emissions Gap Report 2019 showed that to have a likely chance of meeting the Paris Agreement goals, the cuts in global emissions required per year from 2020 to 2030 are close to 3% for a 2°C target and more than 7% per year on average for the 1.5°C goal. It is still possible to bridge the emissions gap, but this will require urgent and concerted action by all countries and across all sectors,” they explain.
Unraveling 66 million years of climate history
Another report suggests that the Intergovernmental Panel on Climate Change (IPCC) projections for 2300 in the “business-as-usual” scenario will potentially bring the global temperature to a level the planet has not seen in 50 million years. In it, climate scientists have revealed changes in the Earth's climate over the last 66 million years in unprecedented detail, highlighting four distinctive climatic states which have been dubbed hothouse, warmhouse, coolhouse, and our current state, icehouse. It was achieved by bringing together research from 12 international laboratories using sample material from the ocean floor collected over more than five decades of international scientific drilling expeditions. The new dataset, CENOGRID, significantly improves the potential for understanding how the Earth’s climate system evolved since the last great extinction 66 million years ago, which introduced a new Era, the Cenozoic.
The analysis reveals that for the past 3 million years, Earth's climate has been in an icehouse state characterized by alternating glacial and interglacial periods. Modern humans evolved during this time, but greenhouse gas emissions and other human activities are now driving the planet toward the warmhouse and hothouse climate states not seen since the Eocene epoch, which ended about 34 million years ago. During the early Eocene, there were no polar ice caps, and average global temperatures were 9 to 14 degrees Celsius higher than today, says the study published in Science. “Now that we have succeeded in capturing the natural climate variability, we can see that the projected anthropogenic warming will be much greater than that,” writes co-author James Zachos, distinguished professor of Earth and planetary sciences, and Ida Benson Lynn Professor of Ocean Health at University of California Santa Cruz.
Co-author Dr Anna Joy Drury from University College London explains that the team used CENOGRID to understand what Earth’s normal range of natural climate change and variability is and how quickly the planet recovered from past events. “While we show that the Earth previously experienced warm climate states, these were characterised by extreme climate events and were radically different from our modern world. Since the peak warmth of the Hothouse, Earth’s climate has gradually cooled over the last 50 million years, but the present and predicted rapid anthropogenic changes reverse this trend and, if unabated, far exceed the natural variability of the last 66 million years.”