Rapid Cuts in GHG Emissions Needed to Limit Global Warming to 1.5°C IPCC

Limiting global warming to close to 1.5°C or even 2°C will be impossible unless there are immediate, rapid, and large-scale reductions in greenhouse gas (GHG) emissions, the Intergovernmental Panel on Climate Change (IPCC) has warned.

In its Climate Change 2021: The Physical Science Basis report, IPCC said the Earth would warm by 1.5°C in all scenarios. Even in the most ambitious emissions pathway, it will reach 1.5°C in the 2030s, overshoot to 1.6°C, before the temperature declines to 1.4°C at the end of the century.

Limiting further climate change would require substantial and sustained reductions in GHG emissions. Without net zero CO2 emissions and a sufficient net negative CO2 emission to offset any further warming, the climate system will continue to warm.

Earlier this year, the UN Environment Programme had released a report that said nations must boost their efforts to adapt to the changing climate scenario to avoid dire consequences in the future. The UNEP Adaptation Gap Report 2020 stated that about 72% of countries had adopted at least one national-level plan for adaptation and most developing countries have one in the works.


According to the report, scientists are observing drastic changes in the Earth’s climate in every region and across the whole climate system. Many of the changes observed, like rising sea levels and polar ice cap melting, are anomalous and are irreversible for the foreseeable future.

The report, compiled by 234 experts from 66 countries in over 4,000 pages, outlines the processes in human-induced climate change, rising temperatures, projections for the future.

According to the report, strong and sustained reductions in CO2 emissions and other greenhouse gases (GHG) would limit climate change. While benefits for air quality would come quickly, it could take at least three decades to see global temperatures stabilize.

“This report reflects extraordinary efforts under exceptional circumstances,” said Hoesung Lee, Chair of the IPCC. “The innovations in this report and advances in climate science that it reflects provide an invaluable input into climate negotiations and decision-making.”

Expeditious Temperature Rise

Human activities are responsible for approximately 1.1°C of warming since the latter part of the 19th century. Global temperature is expected to increase by or exceed 1.5°C when averaged over the next two decades. This assessment is based on improved observational datasets to assess historical warming and progress in scientific understanding of the response of the climate system to human-caused GHG emissions.

“This report is a reality check. We now have a much clearer picture of the past, present, and future climate, which is essential for understanding where we are headed, what can be done, and how we can prepare,” said IPCC Working Group I Co-Chair Valerie Masson-Demotte.

The report also notes that the Indian Ocean is warming at a higher rate than the global oceans. Half of the sea level rise is contributed by the thermal expansion, a reason for the rise in the sea level over the Indian Ocean region. The report concludes that global mean sea levels will continue to rise over the 21st century, even in the lowest emissions scenarios.

The report predicts that snow-covered areas and snow volumes will decrease in most Hindu Kush Himalayan, and snowline elevations will rise, and glacier volumes will decline. This is worrisome as Hindu Kush Himalaya Region is a crucial water supply source for millions of Indians.

Ubiquitous Changes Observed

Global warming directly determines many of the characteristics of climate change, but what people experience is often very different from the global average. Temperatures over land are soaring and are more than the global average and doubles in the Arctic.

“Climate change is already affecting every region on Earth in multiple ways. The changes we experience will increase with additional warming,” said IPCC Working Group I Co-Chair Panmao Zhai.

The report projects that in the coming decades’ climate changes will increase in all regions. An increase of 1.5°C will cause increasing heat waves, longer summers, and shorter winters. A 2°C increase would have devastating effects such as reaching critical tolerance thresholds for agriculture and health.

Climate changes effects are far-reaching and are not just limited to a rise in temperature. Its effects vary from region to region, sometimes diametric. Climate change is intensifying the water cycle, bringing intense rainfall and flooding. In sharp contrast, it is also the reason why many regions are witnessing intense drought.

Changes to monsoon precipitation are expected, with high latitudes receiving increased precipitation. At the same time, in large parts of the subtropics, it is projected to decrease. Coastal areas will see continued sea-level rise throughout this century, furthering frequent and severe coastal flooding in low-lying areas and coastal erosion.

Further warming will amplify permafrost thawing and the loss of seasonal snow cover, melting of glaciers and ice sheets, and loss of summer Arctic sea ice. Oceans will get warmer with frequent marine heatwaves, ocean acidification, and reduced oxygen levels, all linked to human influence. These changes affect both ocean ecosystems and the people who rely on them. They will continue throughout at least the rest of this century.

“Stabilizing the climate will require strong, rapid, and sustained reductions in greenhouse gas emissions and reaching net-zero CO2 emissions. Limiting other greenhouse gases and air pollutants, especially methane, could have benefits both for health and the climate,” said Zhai.

Changes in the climate system resulting from past, present, and future human activities will continue long into the future, even with strong reductions in GHG emissions. Some aspects of the climate system, including the terrestrial biosphere, deep ocean, and the cryosphere, respond much more slowly than surface temperatures to changes in GHG concentrations. As a result, there are already substantial committed changes associated with past GHG emissions. For example, the global mean sea level will continue to rise for thousands of years, even if future CO2 emissions are reduced to net zero.

Recently, the Economic Survey for 2021 had revealed that India would require around $206 billion (~$15 trillion) between 2015 and 2030 to fight climate change.