Humans have ‘indisputably’ caused global warming by emitting greenhouse gases, says scientists

Credit: Adobe Stock
Credit: Adobe Stock

Reports published in recent years leave no doubt about human responsibility for contemporary global warming. 'It is indisputable that humans have caused global warming by emitting greenhouse gases,’ say members of the Climate Crisis Advisory Team at the Presidium of the Polish Academy of Sciences.

Broad discussions on the Internet were triggered by information published last week in PAP, obtained from the Polish Geological Institute, according to which 'on a global scale, the human impact on the climate is small, but it may be significant locally'. The Polish Geological Institute reported that 'the impact of increased greenhouse gas emissions (on climate - ed. PAP), primarily as a result of the burning of fossil fuels by humans, is significantly overrated because the role of parallel warming caused by natural factors is not taken into account'. 

According to the Polish Geological Institute scientists, future climate changes and their effects can be predicted by comparison with reconstructions of the past changes, and 'the modern warming trend is associated with the transition period from the cooling of the Little Ice Age, which ended in the first half of the 19th century. In their opinion, 'the temperature increase on Earth during this time did not exceed 1 degree Celsius, so the temperature is currently still lower than in the maximums of previous warming periods such as the ones during the Middle Ages, the Roman period and the Bronze Age'.

For the vast majority of scientists, however, human influence in accelerating climate change is beyond question. The statement that 'climate change is caused primarily by human activity' is supported by the authors of over 99.9 percent of peer-reviewed scientific publications on climate. Such conclusions result, for example, from meta-analyses of over 88,000 scientific reports from 2012-2020 (presented in Environmental Research Letters in 2021).

Also in a statement sent to PAP this week, , scientists from the Climate Crisis Advisory Team at the Presidium of the Polish Academy of Sciences confirm that people now have access to a lot of data showing the drastic changes taking place in the world.

Carbon dioxide content in the atmosphere has already exceeded 420 ppm and is growing at an unprecedented rate, 'proving that the actions taken so far to reduce emissions are insufficient. Each year of the last decade has been among the ten warmest years since the beginning of regular temperature measurements. The water level in the oceans is increasing at a rate of more than 4.5 mm per year, while in the last decade of the last century it was slightly over 2 mm per year. Heat resources in the ocean in the layer 2 km from the surface are currently increasing at a rate of 1 W/m2, while it was 0.6 W/m2 at the end of the last century. Marine heatwaves already affect 60% of the ocean surface. Greenland has been losing over 250 billion tons of ice annually, and in the record year 2019, the loss of Antarctic ice increased by almost 40% compared to the previous year. Recent years have brought record temperatures. The world record of 54.4 degrees Celsius was recorded on August 16, 2020 in Death Valley, California. The European record of 48.8 degrees Celsius was set on August 11, 2021 in Syracuse, Italy,' the scientists say. 

The culmination of these changes was in 2023, the experts conclude. The average global air temperature was 14.98 degrees C, 0.17 degrees C higher than the previous record from 2016 and 1.45 degrees C higher than the average from 1850–1900, dangerously close to the value of 1 .5 degrees Celsius suggested as the limit in the Paris Agreement. Moreover, from July 3 to July 31, 2023, the average daily temperature on Earth exceeded the previous record of 16.8 degrees C from August 13, 2016. The warmest day was July 6, when the average global temperature reached 17.08 degrees C, exceeding the average temperature for this season in the years 1850–1900 by over 1.5 degrees Celsius.

The scientists recall more records, for example that last year was the first year in the history of regular temperature measurements, in which every day of the year the average daily air temperature exceeded the pre-industrial average by at least 1 degree Celsius; the period from June to December last year was also characterized by previously unrecorded values of average monthly temperatures; in December, the average temperature exceeded the average for the period 1991–2020 by 0.85 degrees C and the average for the period 1850–1900 by 1.78 degrees C. Scientific evidence shows that 2023 was not only be the warmest year on record, but probably the warmest year in 125,000 years.

The thermal exceptionality of 2023 resulted not only from the progressive increase in the concentration of greenhouse gases in the atmosphere, but also the occurrence (immediately after the end of La Niña) of the El Niño Southern Oscillation (ENSO) phenomenon, i.e. the period of positive sea surface temperature (SST) anomalies in the equatorial areas of the Pacific Ocean. High sea surface temperatures outside the equatorial Pacific also contributed to record global average SST values. At the same time, marine heatwaves were an exceptionally common phenomenon last year, recorded in the Gulf of Mexico, the Caribbean, the Mediterranean basin, the Indian Ocean, the North Pacific and much of the North Atlantic.

'We entered 2024 with an unprecedented ocean temperature anomaly, which is a bad forecast for the coming months,’ the experts say.

They add that last year, the range of sea ice around Antarctica reached a record low in February, and the range of sea ice in the Arctic at the March maximum was one of the four lowest at this time of year since satellite observations began in the region.

The year 2023 was also exceptionally warm in Europe. With a temperature 1.02 degrees Celsius higher than the average from 1991–2020, it took second place. Only 2020 was 0.17 degrees Celsius warmer. Values above average persisted for 11 months, and September 2023 was the warmest September on record. Both summer, autumn and winter were exceptionally warm seasons in Europe. The average air temperature in summer was 19.63 degrees Celsius, and in autumn - 10.96 degrees Celsius.

The scientists emphasise that warming has also accelerated in Poland. The rate of temperature increase in the 30-year period 1991-2020 was significantly higher than in the entire period since 1951. The average temperature in Poland has increased by over 2.1 degrees Celsius since the period 1900-1950, which is more than the global average. According to the Institute of Meteorology and Water Management - National Research Institute, the average annual air temperature in Poland in 2023 was 10.0 degrees Celsius. It was the second warmest year in Poland since the beginning of regular measurements, with a temperature 0.2 degrees Celsius lower than in the record year of 2019. In 2023, the institute issued 19 warnings about the occurrence of climate anomalies related to high temperature values.

For Poland, climate change means not only heat, but also droughts during the intensive vegetation period, which is crucial for food security and the survival of natural ecosystems. The average total area of precipitation in Poland was 656 mm in 2023 and although it was 45 mm higher than the so-called rainfall norm, the most important months for vegetation - May, June and July - were much drier than average, and evaporation, at high temperatures, was higher than normal. Therefore, a strong negative climatic water balance (the predominance of evapotranspiration from the active surface over precipitation) was recorded in a large area of the country. This means that the process of losing moisture resources from the surface layer of the soil continues, which in the near future may lead to a significant decrease in the level of groundwater and water levels in streams, leading to restrictions in access to water for domestic and economic purposes (agriculture and industry).

All measurement data collected in the atmosphere, on land and in the oceans indicate that the global warming process is intensifying, which rapidly increases the probability of triggering a cascade of positive climate feedback that threatens to destabilise the climate system. Some changes in the climate system are already irreversible, and the risk of extreme phenomena and complex threats with significant consequences for humans and the environment is growing rapidly.

To prevent a catastrophe - according to a press release by the Climate Crisis Advisory Team at the Presidium of the Polish Academy of Sciences - we need quick and decisive actions, which include adopting a calendar for phasing out fossil fuels, building an international consensus on clean energy, and undertaking educational activities to build understanding and acceptance of climate policy. (PAP)

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