In a June report, over 60 climate scientists from around the world warned that if current carbon dioxide (CO2) emissions continue at their current pace, humanity will cross the critical threshold of 1.5 °C of warming within the next three years. Can we do anything to reverse the rise in temperature, or is climate catastrophe inevitable?
Experts told Live Science that as soon as humanity reduces greenhouse gas emissions, the possibility of gradually lowering temperatures will emerge—even if the critical threshold is surpassed.
However, Michael Mann, a leading climate scientist at the University of Pennsylvania, believes it’s better to cut emissions now than to try to reverse the temperature increases that have already occurred.
The report emphasized that to achieve the critical target of 1.5 °C set by the Paris Agreement, humanity can emit only 143 billion tons of CO2 into the atmosphere. Given the current rate of emissions, this is not much at all. According to the World Meteorological Organization, we are currently emitting about 46 billion tons of carbon each year.
According to the report, the global temperature is currently 1.2 °C higher than the pre-industrial average. However, our emissions have caused even greater warming that has gone unnoticed because the ocean has absorbed much of the excess heat.
According to the National Oceanic and Atmospheric Administration (NOAA), the ocean will release this additional heat over the next few decades through evaporation and direct transfer, regardless of whether we limit emissions.
This means that even if carbon emissions are reduced to zero today, global temperatures will continue to rise for several decades. Experts predict that an additional warming of 0.5 °C will occur primarily due to the oceans.
Why 1.5 °C?
But why do climate scientists consider 1.5 °C to be a critical threshold? A higher increase in warming is dangerous for the planet, especially for island nations, reminded Kirsten Zickfeld, a professor of climatology at Simon Fraser University in Canada.
According to her, the 1.5 °C threshold is an “indicator of the state of the climate system, at which we feel we can still control the consequences.”
If the temperature exceeds 1.5 °C, a massive amount of additional heat will enter the ocean, which will eventually be released. Crossing this threshold increases the risk of reaching climate tipping points—elements of the Earth system that can rapidly shift to a different state. For example, the Greenland ice sheet could suddenly collapse into the ocean, and the Amazon rainforest could transform into a dry savanna.
All Hope Rests on Revolutionary Technologies and Our Awareness
According to Professor Zickfeld, to slow the rise in temperature, we need not just zero emissions but negative emissions. Zero emissions would mean capturing as much CO2 through natural carbon sinks and negative emissions technologies as we emit. Achieving negative emissions will require systems that extract carbon from the atmosphere and then bury it underground.
If we want to reverse warming, we need to remove more carbon from the atmosphere than we emit, said Professor Zickfeld.
“If we reach 1.6 °C and want to bring it down to 1.5 °C, we will need to remove about 220 billion metric tons of carbon dioxide,” she added.
Currently, natural carbon removal methods, such as tree planting, absorb about 2.2 billion tons of CO2 each year. But this figure needs to be increased by 100 times to lower the critical threshold by even 0.1 °C per year.
Professor Zickfeld does not consider this method optimal. Due to the increasing demand for land, it is highly unlikely that humanity will be able to plant enough forests to reverse global warming.
Most greenhouse gas reduction technologies are currently in the testing phase, making it difficult to determine how effective they will be, the professor noted.
Robin Lamboll, a climate researcher at Imperial College London and co-author of the report, stated that these technologies are also very expensive and will likely remain so for a long time.
The Paris Agreement does not require countries to implement emissions-reducing technologies. However, according to Lamboll, the goal of the agreement—to limit the increase in global average temperature to well below 2 °C—means that governments may decide to ramp up these technologies after the temperature exceeds 1.5 °C.