Global warming threshold will be crossed in 6-21 years- Study

A new report reveals that the world might surpass a dangerous heat threshold by as early as 2027

The threshold for dangerous global warming will likely be surpassed between 2027 and 2042 reveals a new study published in Climate Dynamics. The new threshold is much narrower than predicted by the Intergovernmental Panel on Climate Change’s (IPCC) estimate of between now and 2052.

Researchers from McGill University introduced a new and more accurate way to estimate global projections through 2100. The new approach is based on historical data and a simple model of the system memory based on scaling symmetries.

Scientists have been making climate projections using Global Climate Model (GCM). It is a complex mathematical representation of major climate system components like atmosphere, land surface, ocean, and sea ice and their interactions. The earth’s energy balance between the four components helps to make long-term climate predictions.

More robust and certain than GCM

The new approach used by the researchers has smaller uncertainty and is more robust. According to some climate sceptics, IPCC projections are untrustworthy because they are entirely GCM based. Each GCM has its own climate (“structural uncertainty”) and this leads to very large discrepancies in projection, the study says.

“Our new approach to projecting the Earth’s temperature is based on historical climate data, rather than the theoretical relationships that are imperfectly captured by the GCMs. Our approach allows climate sensitivity and its uncertainty to be estimated from direct observations with few assumptions,” says co-author Raphaël Hébert, from the Alfred-Wegener-Institut, Germany in a statement.

According to the study, due to dire ecological consequences of global warming, better information about climate sensitivity is of extreme importance to meet the urgency of adjusting economic and environmental policies.

A new scaling factor

The researchers performed analysis on five observation records of surface air temperature each spanning at least the period 1880-2014. They introduced a new scaling factor- Scaling Climate Response Function (SCRF) to make projections about Earth’s temperature to 2100.

SCRF is used by the researchers to reconstruct the forced temperature variability over the historical period and make future projections according to Representative Concentration Pathway (RCP) scenario. RCP is a greenhouse gas concentration (not emissions) trajectory adopted by the IPCC.

The study looks into three forcing- solar, volcanic, and anthropogenic forcing. Forcing is the physical process affecting the climate on earth through several forcing factors.

“Our new approach to projecting the Earth’s temperature is based on historical climate data, rather than the theoretical relationships that are imperfectly captured by the GCMs. Our approach allows climate sensitivity and its uncertainty to be estimated from direct observations with few assumptions” says Hébert in a statement.

Variations in predictions from IPCC’s estimates

According to the study, the threshold for dangerous warming 1.5 degree Celsius will likely be crossed between 2027 and 2042 which is much narrower than GCM’s estimates between now and 2052.

The study reveals that between 1860-2000 the temperature variability observed by SCRF track closely to that of IPCC. There is a small gap between the two over the 1915-1960 period when the IPPC’s predictions were “consistently warmer” compared to SCRF.

After 2000, the SCRF predicted lower warming than IPCC. The overshoots in IPCC’s predictions are contributed to a combination of factors mainly errors in volcanic and solar input, representation of aerosols and evolution of El-Niño (a climate pattern that describes the unusual warming of surface waters in the eastern tropical Pacific Ocean).

Over the 2043-2100 period, the SCRF projections are similar to that of IPCC.

To avert a 1.5-degree Celsius warming, the study suggests a drastic cut in emission similar to RCP 2.6.

RCP 2.6 requires that carbon dioxide (CO2) emissions start declining by 2020 and go to zero by 2100. It also requires that methane emissions (CH4) curtail to approximately half the CH4 levels of 2020, and that sulphur dioxide (SO2) emissions decline to approximately 10% of those of 1980-1990.

Tipping points to improve future projections

The study assumes a linear stationary relationship between forcing and temperature, abandoning the non-linear interactions which can arise once the system evolves.

“In particular, so-called tipping points could be reached in the coming century which would lead to a breakdown of the linear model proposed,” says the study.

Such tipping points are not observed in GCM also but the study claims that there is a need to study these points to improve future projections. The researchers have assumed in the study that “increased variability in the climate regime to be strictly a result of forcing,” excluding internal modes of variability. To have a better understanding of low-frequency natural variability, the study advocates the use of paleoclimate archives which consist of geologic (like sediment cores) and biologic (like tree rings) materials that preserve evidence of past changes in climate.

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