Climate clock is ticking: Act before it’s too late

Last month, President Donald Trump signed an executive order directing the US to withdraw once again from the landmark Paris Agreement. This decision comes amidst the growing concerns over global warming, with a new study suggesting that greenhouse gas (GHG) levels have already surpassed projections.

The study titled Global Warming Has Accelerated: Are the United Nations and the Public Well-Informed?, by renowned climate scientist James E. Hansen and his colleagues, also states that limiting global temperature rise to well below 2 degrees Celsius – a target set by the Paris Agreement – is now “an implausible scenario”.

The study was published in the Journal Environment: Science and Policy for Sustainable Development. It concludes that the net-zero target of CO₂ emissions by 2050 is unrealistic. Let’s examine key findings of the study and their impact on the evolving climate change scenario alongside the previous projections by UN climate bodies.

The environmental paradox  

Factors affecting the Earth’s energy balance are known as climate forcing. These factors can be natural like solar variability (due to Earth’s orbital cycle) and large volcanic eruptions, or human-induced such as greenhouse gases (GHGs), aerosols, or land-use changes.

The study by Hansen and his colleagues suggests that the recent increase in Earth’s energy imbalance and the acceleration of global warming can be attributed, in part, to the decline in emissions from shipping. Ships that burn high-sulfur fuel release sulfate aerosols into the atmosphere, which reflect sunlight back into space. This helps in reducing the amount of solar radiation absorbed by the Earth and having a temporary cooling effect on the planet.

It may be noted that by 1992, when the United Nations Framework Convention on Climate Change (UNFCCC) was adopted, climate scientists had understood that anthropogenic activities were affecting the climate mainly in two ways: GHGs and aerosols (tiny particles suspended in the air).

While GHGs like CO₂ contribute to global warming by trapping longwave radiation emitted from the Earth’s surface, most of the human-induced aerosols generated through the burning of fossil fuel and biofuel increase the reflection of incoming solar radiation and thus have a cooling effect for the Earth’s surface. 

However, while these aerosols have a cooling effect on the Earth’s surface by reflecting solar radiation, they also increase air pollution and cause respiratory and cardiovascular diseases in millions of people. In 1992, the warming effect of GHGs and the cooling effect of aerosols were roughly balanced. But overall global temperature change is determined by the combined effects of GHGs and aerosols. 

With the increasing efforts to control pollution and transition to clean energy, the presence of aerosols in the atmosphere, alongside their cooling effect, is also decreasing. A notable example of this is the limits put on the sulfur content in ship fuels by the International Maritime Organisation (IMO) in January 2020. The most substantial impact of this limit was observed in the North Pacific and North Atlantic, regions that earlier contributed the largest amount of sulfate aerosols. 

Criticism of IPCC estimates

The study also suggests that GHGs are now more than double the amount projected in the Intergovernmental Panel on Climate Change (IPCC) – the United Nation’s scientific advisory body. It argues that the net-zero target of CO₂ emissions by 2050 is unrealistic and “implausible”, as present global policies indicate continued high fossil fuel emissions in the near future. 

The study is also critical of many of the estimates and conclusions of the IPCC. It argues that the IPCC has significantly underestimated the cooling effects of aerosols on the planet, which, in turn, led to the underestimation of climate sensitivity. The study also highlights that IPCC models do not fully capture the non-linear impacts of aerosols.

Hansen and his colleagues also estimate that there will be a temperature rise of 0.2-0.3 °C per decade in the next two decades, leading to a +2 °C increase in global temperatures by 2045. Resultantly, the goal of keeping warming under 2 degrees Celsius by the year 2100 is an “implausible scenario”. 

Limiting the global temperature increase to well below 2 degrees Celsius is one of the main goals of the Paris Agreement – a legally binding international treaty adopted in 2015 during the UN Climate Change Conference (COP21) in France. 

The treaty aims at strengthening the global response to climate change through various measures. It strives to keep the global temperature within 1.5 degrees Celsius above pre-industrial levels. The treaty also requires all parties to prepare, communicate and maintain a nationally determined contribution (NDC) and to pursue domestic measures to achieve them. 

Additionally, all parties must meet every five years to assess the collective progress towards the goals of the agreement and to share updates on their individual actions.

‘Point of no return’

However, as the climate crisis escalates, scientists warn of approaching the ‘point of no return’— thresholds beyond which irreversible damage occurs. There can be multiple tipping points. Some of these include – the melting of Arctic permafrost, which would release large amounts of GHGs; the heating and drying of the Amazon rainforest to a point where it can no longer sustain itself, with forest fires releasing much of the stored carbon. 

But the worst of all could be the collapse of the West Antarctic Ice Sheet – the Point of No Return – which would unleash the rise of sea level by several meters. This could happen if the Atlantic Meridional Overturning Circulation, which transfers heat from the Southern Ocean to the Northern Hemisphere, shuts down. 

In such a scenario, heat would not be transferred, leading to further warming of the Southern Hemisphere and the melting of the Antarctic ice sheets. Some climate simulations suggest that this scenario could unfold within this century due to the current rate of greenhouse gas emissions. 

The last time such warming occurred was during the Eemian interglacial period, approximately 1,29,000 to 1,16,000 years ago. Paleoclimatic evidence shows that in this period, Earth’s temperatures were warmer than today – about 2°C higher than pre-industrial levels. These pieces of evidence provide valuable insights into past warm conditions and are crucial for understanding Earth’s future as it continues to get warmer. 

In its 4.6 billion years of history, Earth has experienced several glacial periods, with inter-glacial periods in between. Interglacial periods are characterised by melting ice sheets and glaciers, increasing temperatures, and rising sea levels. The current geological epoch – the Holocene –  extends from approximately 11.7 thousand years ago to the present and represents a “warm period” between ice ages. 

However, due to anthropogenic activities – such as increased emission of GHGs – Earth is getting warmer at a rapid pace.

Need for realistic assessment

Scientific concerns over human-induced climate change are not new. In 1958, Charles David Keeling started precise measurements of atmospheric CO₂, and confirmed that anthropogenic activities were changing the composition of the atmosphere. 

In 1988, Dr. Hansen was associated with NASA and testified before a US Senate committee: “’Global warming has reached a level such that we can ascribe with a high degree of confidence a cause-and-effect relationship between the greenhouse effect and observed warming.” That same year, Time magazine declared Earth “Planet of the Year” due to the growing concerns over extreme climate anomalies.

This underscores the need for focused research to provide a realistic assessment of the climate situation in the coming decade. In addition, a better-informed public alongside the consideration of real-world energy demands in future policies needs to be born in mind when setting achievable targets to bring down GHG emissions.

Post Read Questions

What does the recent study by James E. Hansen and his colleagues reveal about current greenhouse gas levels?

Why do Hansen and his team argue that limiting global temperature rise to below 2 degrees Celsius is “an implausible scenario”?

How have greenhouse gas levels exceeded the projections made by the IPCC and other climate bodies?

What are the key factors contributing to the failure to meet the 2-degree Celsius target?

What changes in policy or global action does the study suggest to address the accelerating climate crisis?

(Abhinav Rai is a Doctoral candidate at the Department of Geography, Delhi School of Economics, University of Delhi.)

Share your thoughts and ideas on UPSC Special articles with ashiya.parveen@indianexpress.com.

Subscribe to our UPSC newsletter and stay updated with the news cues from the past week.

Stay updated with the latest UPSC articles by joining our Telegram channel – IndianExpress UPSC Hub, and follow us on Instagram and X.