According to the National Centers for Environmental Information (NCEI), the average global temperature from September to November 2024 was 1.31 degrees Celsius above pre-industrial levels, ranking as the second warmest in the last 175 years.
The Paris Agreement, established at the COP21 conference, aims to limit the average global temperature increase to 1.5 degrees Celsius by 2030 and achieve net zero emissions by 2050. However, the ongoing rise in temperatures due to human activities is rapidly depleting the carbon budget, making it increasingly challenging to meet these goals.
Temperature Gap
Human activities are widely accepted as the primary drivers of the climate crisis. In 2023, the average global temperature reached nearly 1.45 degrees Celsius above pre-industrial levels, making it the hottest year on record. Scientists attribute this increase to several factors, including the accumulation of greenhouse gases, natural events like volcanic eruptions, and weather phenomena such as El Niño.
Despite this, a gap of approximately 0.2 degrees Celsius remains unexplained. This discrepancy has puzzled scientists, prompting a research group from the Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research, to propose a potential explanation. They suggest that the planet has become less effective at reflecting sunlight, attributing this decline to a decrease in certain types of clouds. This study was published in the Science journal on December 5, 2024.
Albedo and Energy Reflection
The ability to reflect sunlight is referred to as "albedo," and the researchers focused on measuring this phenomenon. They gathered data from various sources dating back to 1940 to analyze changes in the energy budget and cloud cover. Their findings revealed a decrease in the reflection of solar radiation into space, peaking in 2023. This means that more solar radiation and its associated heat are being trapped in the atmosphere, contributing to global warming. This decline helps explain the missing 0.2°C gap.
Decline in Icy Surfaces
In their investigation, the researchers discovered a notable decrease in polar snow and sea ice since the 1970s. These icy terrains play a crucial role in reflecting sunlight. The decline in sea ice and Arctic snow accounted for about 15% of the planet's albedo loss. Additionally, they observed a significant reduction in Antarctic ice since 2016. Through simulations, the researchers found that without the decline in albedo since December 2020, the average temperature in 2023 would have been approximately 0.23°C lower.
Fewer Clouds
The researchers also examined the impact of cloud cover on temperature regulation. Clouds reflect sunlight, contributing to cooling. However, certain types of clouds in the upper atmosphere can produce a warming effect due to heat emitted from the atmosphere. While these upper clouds also provide some cooling, their influence can be similar to that of greenhouse gases. In contrast, low clouds have a stronger cooling effect. Researchers discovered a decline in the number of low clouds, resulting in a loss of their cooling benefits, leading to rising temperatures.
To understand the decrease in low clouds, scientists looked into the drop in aerosol concentrations from human activities, as aerosols play a role in cloud formation and reflect sunlight. Additionally, global warming itself further contributes to the reduction in cloud cover.
The study's authors anticipate that average temperatures will continue to rise in the coming years, likely surpassing the Paris Agreement target of 1.5 degrees Celsius ahead of schedule. They emphasize the importance of implementing adaptation measures to mitigate extreme weather events and stress the need to reduce greenhouse gas emissions through effective strategies.
