Study finds increase in tropospheric water vapor amplifies global warming and climate change
Focused on years from 1980 to 2020
image: Observed and model projections of water vapor under three different future climate scenarios SSP126, SSP245, and SSP585 using the results from the CMIP6 model CNRM-CM6-1HR for the period 1980 to 2100. Here, NML and SML indicate northern midlatitudes and southern midlatitudes, respectively.
Credit: Vikas Kumar Patel and Jayanarayanan Kuttippurath, CORAL, Indian Institute of Technology Kharagpur
Climate change fueled by global warming is one of the biggest issues facing Earth right now. High emissions of green-house gases are the primary reason for the climate warming. So, researchers conducted a study using measurements and reanalysis data to examine the variability and long-term changes in global tropospheric water vapor. They analyzed the factors affecting the variability and trends in water vapor and quantified the impact of changes in water vapor on temperature by estimating its radiative effects. Their study provides new evidence of global change associated with the increase in global water vapor.
Their research was published in the journal Ocean-Land-Atmosphere Research on July 6, 2023.
Among the greenhouse gases, atmospheric water vapor is the most abundant, has a large influence on the radiation budget of Earth, and plays a decisive role in regional weather processes. The troposphere is the lowest layer of Earth’s atmosphere. “The troposphere contains approximately 99 percent of the atmospheric water vapor, and is directly connected to the global energy budget and hydrological cycle. It is at the center of all major atmospheric processes, and plays an essential role in the formation of clouds, tropical cyclones and thunderstorms,” said Professor Jayanarayanan Kuttippurath from CORAL, Indian Institute of Technology Kharagpur.
Understanding and monitoring atmospheric water vapor changes are critical for assessing climate change, and feedback mechanisms in the models. Since water vapor is the most abundant greenhouse gas, and is increasing globally, the team wanted to examine its spatio-temporal variability and its impact on global temperature. They chose to examine the problem by looking at the variability and changes in water vapor over recent decades across latitudes.
The annual climatology of global tropospheric water vapor varies from 5 to 60 kg/m2 across different regions. There is a strong seasonal cycle in both the southern and northern hemispheres, except in the tropics. The highest values occur in summer and the smallest values in winter.
The team used satellite, radiosonde, and reanalysis data to investigate the long-term changes in global tropospheric water vapor. They assessed the impact of changes in water vapor on the regional and global climate with respect to its radiative feedback, analyzing the years from 1980 to 2020.
Their study shows a global increase in tropospheric water vapor, at about 0.025 to 0.1 kg/m2/year, during the years analyzed, with a notable increase in the Arctic because of the high rise in temperature there. Considering that water vapor is a strong greenhouse gas, it would increase regional and global temperatures through radiative effects, approximately −5 to −70 W/m2 at the surface, depending on the region.
The model projections for future high-emission scenarios show a large increase in atmospheric water vapor. “It is also expected to increase significantly by the end of the 21st century, with high amounts in the polar regions, approximately twice the current values. Furthermore, an increase in atmospheric water vapor amplifies the warming caused by other greenhouse gases, which would further intensify global warming and adversely affect the global and regional climate,” said Vikas Kumar Patel, CORAL, Indian Institute of Technology Kharagpur.
“This is a great concern for global and regional climate, as the rise in water vapor would further augment global warming and phenomena, such as the Arctic amplification,” said Patel.
With water vapor increasing in most regions, as the researchers look ahead, they would like to explore the implications for this. “One aspect, for instance, is that we have observed an increase of water vapor in some of the global deserts, and consequently, there is greening in those deserts . We would like to explore this phenomenon in detail, and also the energy budget and socio-economic changes in those desert regions,” said Kuttippurath.
The researchers are Vikas Kumar Patel and Jayanarayanan Kuttippurath from CORAL, Indian Institute of Technology Kharagpur.