Volcanic eruptions in tropical regions may have a greater influence on cooling the Earth’s climate than previously understood, according to new research published in the journal Geophysical Research Letters. Scientists say these eruptions can release gases into the upper atmosphere, creating tiny reflective particles that reduce the amount of sunlight reaching the planet’s surface.
Explosive volcanic eruptions release large quantities of sulphur dioxide into the stratosphere. The gas reacts with water vapour and oxygen to form tiny sulphuric acid aerosol droplets. These particles reflect and scatter sunlight back into space, temporarily lowering global temperatures for months or even years.
A well known example is the 1815 eruption of Mount Tambora in Indonesia which contributed to the 1816 climate event known as the “Year Without a Summer”, causing unusually cold conditions across parts of the world.
Researchers led by Dr Zachary McGraw of Columbia University used a NASA climate model to examine whether the location of a volcanic eruption determines how much cooling occurs in the Northern Hemisphere.
Earlier studies suggested that eruptions in the middle latitudes, between 30 and 70 degrees, could produce significantly stronger cooling than tropical eruptions of similar magnitude.
However, the new research found no clear evidence of such a large difference. The simulations indicated that cooling from extratropical eruptions could be, at most, around twice as strong rather than the 7.5 times suggested by previous studies.
Scientists explained that aerosols from tropical eruptions can spread across both hemispheres through atmospheric circulation, while particles from middle latitude eruptions tend to remain concentrated in the Northern Hemisphere.
Tree Rings Help Reveal Historical Climate Changes
To test their findings researchers examined historical climate records, including tree ring data. Trees generally produce wider growth rings during favourable warm or wet conditions and narrower rings during colder or drier periods.
The team studied evidence associated with historical eruptions, including events in Iceland in 1783, the middle latitudes in 536 CE and Alaska in 43 BCE. These records were compared with climate simulations and evidence from tropical eruptions.
The findings showed that Northern Hemisphere cooling was more frequently associated with tropical volcanic eruptions. The researchers also found that aerosols from extratropical eruptions generally remain in the atmosphere for shorter periods, often up to nine months, compared with as long as three years following tropical eruptions.
This difference is linked to the lower altitude at which gases are released, greater removal of aerosols by rain and snow, and atmospheric circulation patterns that transport particles towards the poles.
Findings Could Improve Climate Risk Predictions
The research offers important insights into the temporary cooling effects of volcanic activity and how they interact with longer term climate change driven by factors such as human caused greenhouse gas emissions.
A better understanding of volcanic aerosols could help scientists improve climate models, assess potential disruptions to agriculture and food production, and prepare for risks to global food security.
Researchers say understanding how major eruptions influence temperatures and atmospheric conditions is essential for predicting climate.related challenges and planning for their wider social and economic consequences.