The Cold tongue, El Nino, and climate change

Two years ago, the U.N. Intergovernmental Panel on Climate Change (IPCC) released their latest report on Climate Change   in which the IPCC greatly narrowed the likely future temperature rise. Nonetheless, emissions of carbon dioxide have been rising by about 1% per year on average for the past decade (with a slight pull back during the pandemic). Though, renewable energy use has been expanding rapidly, much of the renewable energy is being deployed alongside existing fossil energy, not replacing it.  

All the climate models tie the rise in global temperatures to concentrations of atmospheric carbon dioxide and this is still happening. The planet has warmed 1.1 degrees C since the late 19th century and is expected to warm an additional 0.4 degrees C in the next 20 years. Just to make this point, this past July has been reportedly the warmest month in history.

Mankind in their burning of fossil fuels and covering the earth with concrete is responsible for this rise in temperature. No actions that nations are likely to take can change this trajectory we only have some hope of moderating it.  That was the key finding of the IPCC report. Total CO2 emissions for planet earth have passed 40.6 billion tonnes of CO2 (GtCO2) per year.

The Pacific, the largest ocean on earth, has a surface larger than all the continents combined. The weather on the planet is impacted by the El Nino Southern Oscillation where the winds across the Pacific Ocean move the planet between La Nina and El Nino conditions every few years and the Decadal Oscillation a much longer pattern that appears to happen over 20-30 years.

As pointed out in an excellent article by Madeleine Cuff last week in New Scientist. The massive climate models created to model our plant predict that as a result of climate change, the surface of the Pacific Ocean should be warming, but hidden in the natural large variability of the Pacific Ocean is an oddity.  Between 1980 and 2022 the planet’s sea surface temperatures increased faster than the Earth’s surface temperature. However, there is an area in the eastern Pacific Ocean emanating from the coast of south America that has been cooling defying all the models. That area is known as the cold tongue.

While the eastern Pacific Ocean has always been (as far as we know) cooler than the western Pacific Ocean, this difference has increased by about 10% (about half a degree Celsius). This oddity may have significant impact on how quickly the planet warms and the resultant weather patterns. If the eastern Pacific Ocean were to suddenly flip to a warming pattern, this could change the base state of the climate to La Nina conditions. Climate resilience plans would need to change to respond to unanticipated extensive and permanent drought in the U.S. Southwest and the Horn of Africa.

Scientists do not understand the cause of the cold tongue and how long it may continue. It matters, in understanding the future planet climate conditions and how severe they are. If it continues the cold tongue could reduce the anticipated global warming by about 30% according to sone researchers. Many efforts have been made to reconcile the discrepancies between climate model projections and real world observations (Solomon and Newman 2012, L'Heureux et al 2013a; Luo et al 2018, Chung et al 2019) with various theoretical arguments. 

Researchers at Lamont-Doherty Earth Observatory at Columbia University have been studying the Pacific Oscillation and climate modeling. Their work indicates that not all climate models include Antarctic meltwater in their calculations and some have trouble correctly reflecting changes to sea temperatures, winds and currents in the Southern Ocean. As a result, warming projections for this century by current global climate models may be overestimated. That would be good news.

Other scientists believe that the current climate models will be proven correct eventually. The eastern Pacific will eventually flip to warming because of all the greenhouse gasses mankind continues to pump into the atmosphere. Now, to try and solve the mystery an international working group formed this year to study the cold tongue. To predict what will happen next, we first need to understand what is happening now.

Read the research from Lamont-Doherty Earth Observatory, the linked studies above and the full article in New Scientist if you are interested in learning more.