Environmental imperative of net zero

Climate change is the existential threat of our lifetimes. Fundamentally, certain gases in the atmosphere called greenhouse gases (GHGs) trap the heat of the sun. When concentrations of these gases increase, more heat is trapped, leading to an increase in the average temperature of the earth. Global warming is a long-term trend in the average temperature across all points on the globe. It is not an individual weather event, like a chilly weekend or a hot summer’s day, in a single location. 

The primary GHGs in order of their damage are carbon dioxide, methane, and nitrous oxide. The latter two have a higher heat-trapping ability than carbon dioxide molecule-for-molecule, but fortunately, they are present in much lower concentrations. Carbon dioxide concentrations were between 180 and 280 parts per million for the last 800,000 years but increased to 420 parts per million in the last 100 years. While agriculture and waste contribute to GHGs, the combustion of fossil fuels to slake mankind’s insatiable thirst for energy causes the majority of harmful emissions.

Annual GHG emissions total 59 billion tons, an amount so large that the gases simply cannot be absorbed by the oceans and the land. The resulting increased concentration in the atmosphere drives higher temperatures. The earth has already warmed 1.2 degrees Celsius, with above-average warming in the oceans and at higher latitudes. There is nowhere on earth that has not experienced climate change. Climate impacts will get worse before they get better, but there are still opportunities to reduce risk. 

In 2023 alone, fifteen Indian cities experienced five or more days of extreme heat waves, and twelve cities had 100 or more days of above-average temperatures. Due to warmer oceans, ice caps are melting and ocean water is expanding, leading to rising seas. Mumbai, Cochin, Bhavnagar, Vishakhapatnam, Mangaluru, and Chennai are the Indian cities most likely to be inundated in this century.

Warmer air holds more moisture, leading to more frequent and extreme weather events like bomb cyclones, storms, floods, and droughts. Excess carbon dioxide absorption is acidifying oceans, bleaching coral reefs, and destroying marine habitats. Many species are migrating to higher latitudes and facing new predators and diseases, leading to the extinction of species and the loss of biodiversity. Crop failures, forest fires, climate migration, new disease vectors, and the loss of fishing livelihoods exert profound human impacts.

Climate scientists mandate that we limit global warming to 1.5 degrees Celsius. Doing so will allow us to adapt to and mitigate the worst impacts of climate change. Beyond 1.5 degrees Celsius, well-understood phenomena like sea-level rise will get worse. Additionally, we will trigger “tipping points” that fundamentally upset nature’s balance. A tipping point is a natural phenomenon with out-of-control positive feedback. For example, the melting of ice caps exposes the brown earth beneath. The darker earth absorbs more heat, causing more ice to melt and exposing even more brown earth. The resulting rise in sea levels and temperatures could be disastrous beyond our current comprehension.

To minimise the possibility of such an outcome, we must urgently cut our GHG emissions until we achieve “net zero.” Net-zero implies that we reduce GHG emissions as much as possible and then offset what remains by planting additional forests, as an example.

Researchers have come up with a precise “global carbon budget” of 280 billion tons of GHGs to limit global warming to 1.5 degrees Celsius. This works like any other budget. We add up the GHG emissions each year, starting in 2024, until we achieve net zero, at which point there is nothing to add any more. This final cumulative carbon “spending” should be under budget to stave off the worst impacts of climate change. At the present rate, we will blow our budget before 2030. Analysis shows that to limit warming to 1.5 degrees Celsius, the world must cut emissions in half by 2030 and to zero by 2040.

Many countries have pledged to reach net zero by 2050, while India’s target is 2070. None of these is sufficient, but sooner is, of course, better. India needs an urgent and concerted effort to target net zero much earlier than 2070 and as close to 2040 as possible.

Can India accelerate its plan? At what cost? Why should we bother? The answers may surprise you. Stay tuned to this series. 

(Visweswariah is VP, cure100.org, and Muralidharan is an R&D specialist, IIT Madras)
(This is the second in a series of seven articles on climate change and net zero)