Weather Bee: How to track the climate crisis in pleasant weather

As long as the earth gains energy, some part of it will undergo changes that affect the earth’s climate

With the rainiest May in recorded history and recurrent cloudy weather at least from the middle of June, parts of India might feel that the climate crisis is on hold. In fact, this may be the case even when examining the global average temperature. The probability that 2025 will breach the warming threshold of 1.5°C – global leaders agreed to keep long-term warming from pre-industrial levels below this number in the 2015 Paris Agreement – is now low, similar to 2024. Berkeley Earth, a US-based non-profit organisation that publishes a global temperature dataset showing a higher level of warming than other datasets, reported on July 17 that the probability of 1.5°C warming in 2025 was 18% after factoring in the data up to June. This number was 52% when the non-profit had published its analysis up to April. None of this, however, means that the climate crisis is on hold. Here is why.

The Baltic Sea, which is shared by the EU and Russia, now rarely freezes over because of climate change, depriving seals of sanctuaries to rear their cubs. (AFP)

Cool weather in your locality does not mean cool global weather or climate

Before explaining why less than 1.5°C warming in 2025 does not mean that the climate crisis is on hold, it might be useful to see that cool local weather does not mean cool global weather. For example, the year up to June is ranked the eighth warmest for India by mean temperature, whereas the global average of temperature is ranked the second warmest. Moreover, as the accompanying chart shows, the global average temperature does not increase linearly. This means that one year of sequential cooling is no guarantee of long-term cooling. For example, while 2021 and 2022 are ranked 10th and eighth warmest in NASA’s GISTEMP dataset, all the 10 warmest years up to 2024 are the ten years of the 2015-24 decade.

Air is not the only thing getting warmer due to the climate crisis

To be sure, what is commonly known as temperature is just the temperature of air two metres above the surface. This means that other things – such as water, land, or the rest of the atmosphere – can get warmer even while there is a relative cooling in 2m temperature. Therefore, another metric commonly tracked along with air temperature is the sea surface temperature (SSTs), since it indicates climate crisis-related changes in another large part of the earth.

Some signs of climate crisis come without a change in temperature

While air temperature and SSTs receive widespread attention, perhaps because they explicitly show warming, not all changes due to the climate crisis may be evident as a change in temperature. Some of that change is also manifested as phase change (or change in the state of matter) without any change in temperature. For example, 334 kilojoules (kJ) of energy given to one kilogram of ice at 0°C will convert it to water without any change in temperature. This is one reason why air temperature and SST need not increase every year: because earth can also lose vast amounts of ice and snow instead. For example, polar ice (this is tracked regularly because it is the largest concentration of ice and also helps in reflecting sunlight) was at its second lowest level for June this year, when both average air temperature and SST were ranked third highest.

The combination of SST warming and ice melt increases sea levels

All three metrics discussed above show some fluctuation year-on-year because not all three parts – 2m air, sea surface, and polar ice -- need to gain energy every year. Clearly, a measure that combines some of these metrics will show less fluctuation. One such measure is the average sea level. This shows less fluctuation because it combines the melting of polar ice (which flows into the ocean), some ice melt even from glaciers (which can flow into the ocean through rivers), and the change in temperature of the oceans even below the surface (which leads to the volume of the oceans expanding). As the accompanying chart shows, average sea level has gone up almost in a straight line.

All these changes are combined in a single number

The above discussion should make it clear that none of the metrics described above can fully track the climate crisis. For example, none of them track what is happening to land temperatures, or the phase change from liquid water to water vapour, or even the temperature of different layers of the atmosphere. One way to tide over this problem, which would otherwise entail measuring every inch of earth inside out, is to look at earth as a whole instead of measuring its constituent parts. Scientists do this by tracking the flow of energy at the top of the atmosphere. While the exact explanation for this involves thermodynamic laws, it is sufficient to know here that if the temperature and phase change of the earth’s constituent parts add up to a non-zero number, it will change earth’s energy. The data for earth’s energy shows it has been increasing continuously irrespective of how a particular year fared in terms of air/sea temperatures, sea level, or polar ice. While earth still loses energy in particular months, the net energy change for earth over the course of 12 consecutive months has always been positive after September 2002. In other words, at the end of every year since 2002, earth has had more energy than the previous year.

This is why pleasant weather in a particular month or a year’s worth of cooling means little to nothing in terms of the climate crisis. As long as the earth gains energy, some part of it will undergo changes that affect the earth’s climate, a process that has been underway since the Industrial Revolution, and only gathered pace as fossil emissions increased. We are experiencing it in a dire way now only because we are close to levels of irreversible change for a large majority of earth, such as a warming of 1.5°C in air temperatures.