A recent study offers evidence that humans are the cause of climate change and shows how human activities have altered the Earth's atmospheric temperature. Scientists have highlighted temperature differences between the troposphere and the lower stratosphere as evidence of the impact of human activities on climate.
Study identifies human-induced climate change
The study reveals that the fingerprint or evidence is based in the mid to upper stratosphere, which lies between 25 and 50 kilometres above the Earth's surface, and this improves the ability to detect human-induced changes.
This identification is crucial as anthropogenic carbon dioxide (CO2) levels increase in the mid and upper stratosphere, adding to noise levels from natural internal variability over short time scales, leading to different patterns of signal and noise and leaving a significant cooling effect.
Daily weather, El Niño and La Niña precipitation variations, annual and long-term natural fluctuations in weather are examples of tropospheric noise. In contrast, continuously variable noise is lowest in the upper stratosphere, making the signal from anthropogenic climate change more detectable.
Due to exhaustive analysis of evidence in the upper stratosphere, longer temperature records and better climate models, it is now nearly impossible to explain the thermal composition of Earth's atmosphere by natural causes alone, according to the study.
According to the study's lead author, Benjamin Santer, an assistant scientist in the Department of Physical Oceanography at Woods Hole Oceanographic Institution (WHOI) in Massachusetts, USA, the anthropogenic cause of the CO2 rise is the clearest evidence for climate change.
Santer, who has worked on climate fingerprinting for more than 30 years, said: "This research debunks the misguided claim that climate change shouldn't be taken seriously because it's completely natural."
Carbon dioxide's dominant role confirmed
As the world grapples with climate change, it's important to be as sure as possible about the role of carbon dioxide, said Susan Solomon, the Martin Professor of Environmental Studies at the Massachusetts Institute of Technology.
Due to advances in satellite data and simulations, the mid to upper stratosphere, previously not studied in depth, can now be further analyzed. This study is the first to identify patterns of anthropogenic climate change in this layer, according to the scientists involved.
The scientists claimed that these distinctive fingerprints can detect the effects of anthropogenic climate change caused by CO2 within 10 to 15 years. Study co-author Qiang Fu, a professor in the University of Washington Department of Atmospheric Sciences, emphasized the importance of this finding.
"Our observations not only show a warming of the troposphere but also provide unique evidence for severe cooling in the upper stratosphere, also showing the dominant role of carbon dioxide in climate change," Solomon said.
In 2021, the average global CO2 concentration was about 415 parts per million (ppm), compared to 280 ppm before the Industrial Revolution.
Concerns over human impact on climate
The study shows that the real world has changed in ways that cannot be explained by natural causes alone, Santer said.
Santer said that while it's intellectually rewarding to be able to extend fingerprints higher up in the atmosphere to test Manabe and Wetherald's prediction, it's also deeply concerning.
"As someone trying to understand the kind of world that future generations will inhabit, these results are very concerning to me. We are fundamentally changing the thermal structure of Earth's atmosphere, and there is no joy in acknowledging that," Santer said.
"This study shows that the real world has changed in ways that simply cannot be explained by natural causes," Santer added. "We now face important decisions, in the United States and around the world, about what to do about climate change. I hope those decisions are based on our best scientific understanding of the reality and severity of human effects on climate."
Rapid and large changes in warming
Throughout Earth's history, its climate has undergone various changes. In the past 650,000 years, there have been seven cycles of glacial advance and retreat, with the last ice age ending about 11,700 years ago, ushering in the modern climate era and human civilization.
Most of these changes in climate are attributed to minor variations in Earth's orbit that affect the amount of solar energy the planet receives. However, the observed warming in recent decades is too rapid to be linked to changes in Earth's orbit and too large to be caused by solar activity.
Evidence from ice cores taken from Greenland, Antarctica, and tropical mountain glaciers demonstrate that Earth's climate responds to changes in greenhouse gas levels. Ancient evidence can also be found in tree rings, ocean sediments, coral reefs, and sedimentary rock layers.
The evidence from the past, known as paleoclimate evidence, reveals that current warming is occurring at a rate about ten times faster than the average warming during ice age recoveries. Carbon dioxide produced by human activity is increasing more than 250 times faster than natural sources after the last ice age.
Observable evidence of rapid climate change includes:
- Global temperature rise
- Warming ocean
- Shrinking ice sheets
- Retreating glaciers
- Decreased snow cover
- Sea level rise
- Declining arctic sea ice
- Extreme weather events
- Ocean acidification
Fossil fuel fingerprinting
How do we know for sure that humans are causing global warming? The answer lies in the science of carbon dioxide (CO2) emissions from fossil fuels.
These emissions have a specific ratio of carbon isotopes, called δ13C, which is only present in the atmosphere when coal, oil or gas is burned.
Since the 1880s, δ13C has changed in a way that can only be explained by an increase in CO2 from fossil fuels. This is a clear indication that human activities, particularly the burning of fossil fuels, have been the main cause of rising CO2 levels since pre-industrial times.
The combination of natural and human-induced climate drivers has contributed to the observed warming over the past 50 years. Studies indicate that human activity is responsible for more than 50% of the warming observed since 1951.
Attribution science has become more sophisticated, allowing scientists to quantify the increased probability and intensity of extreme weather events, such as tidal waves of heat and downpours, due to human activity. caused climate change.
Research has shown that climate change doubled the risk of the 2003 European summer heat wave and made record rainfall in Texas during Hurricane Harvey three times more likely.
Fingerprints of climate change have also been detected in global daily weather patterns since 2012 and annual patterns since 1999.
While some extreme weather events are more readily attributable to global warming than others, authoritative scientific institutions and government agencies confirm the validity of attributing events individual extremes to human-caused climate change.
Attribution science is the process of determining the cause of a particular event or trend. In the case of climate change, attribution science involves trying to determine the extent to which human activity has caused the observed warming.
Natural factors such as solar radiation, volcanic eruptions, and changes in Earth's orbit have influenced Earth's climate in the past, but these factors cannot explain the observed warming in recent decades. In fact, studies have shown that natural factors would have led to a slight cooling in recent decades if human activities had not contributed to the warming.
One way to determine the cause of the observed warming is to use computer models. These models simulate Earth's climate system and may include different combinations of natural and human drivers of climate change. When models include only natural factors, they cannot reproduce the warming observed in recent decades. However, when models include human activities like burning fossil fuels, they accurately simulate observed warming.
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