“Alarming Yet Encouraging: New Scientific Assessment of Human Impact on Climate”

The latest scientific assessment of how human activity is impacting the climate is both alarming and encouraging. The second “Indicators of Global Climate Change” report, published in Earth System Science Data, provides an annual update on key metrics originally assessed by the Intergovernmental Panel on Climate Change (IPCC). With the next IPCC assessment report not expected until at least 2027, this report fills a crucial gap in tracking climate change.

In 2023, which set a new record for the warmest year, human activity was estimated to have caused a warming of 1.31C above pre-industrial levels. This marks the first time this estimate has crossed the 1.3C threshold, with human-caused warming increasing at a rate of 0.26C per decade. The high rate of warming is attributed to greenhouse gas emissions nearing all-time highs and a reduction in cooling impacts of aerosols as efforts to tackle air pollution intensify.

Despite these concerning trends, there is some positive news. Greenhouse gas emissions have not surpassed pre-pandemic levels, and the rate of increase in CO2 emissions over the past decade has slowed compared to the 2000s. However, emissions rebounded following Covid-induced lockdowns, with CO2 emissions from coal, gas, and non-CO2 gases on the rise.

The report also highlights the impact of human-caused global warming on the Earth’s energy balance, with observations showing a doubling in the rate of heat flow into the Earth’s systems. This has led to a 0.1C increase in global warming over the past four years.

Additionally, the report reassesses the remaining carbon budget, indicating that at current emission rates, the budget for a 50% likelihood of staying below 1.5C would be exhausted within five years. Factors contributing to the record warmth in 2023 are still being investigated, with potential influences from shipping emission reductions, natural phenomena like El Niño, and wildfires.

Looking ahead, the report aims to provide insights into how human activity is shaping the climate system and hopes to inform more ambitious climate action under the Paris Agreement. The next update in 2025 is expected to track progress towards stronger and more ambitious climate targets on a global scale.