July was the hottest month since global temperature measurements began, averaging 1.22 Celsius (degrees) above the preindustrial background period of 1850 to 1900. Temperatures are closing in on the IPCC target of 1.5 Celsius at which a series of natural processes, such as the loss of summer sea ice and collapse of Siberian permafrost, will begin to amplify the temperature increases.
Ominously, Berkeley Earth found that July 2019 was 2.20 degrees (1.22 Celsius) warmer than the 1850 to 1900 average, which is often used as the baseline for preindustrial temperatures. www.washingtonpost.com/...
July’s weather has come as a bit of a shock to climate scientists because temperature peaks in the past have been the result of strong El Niño events which are exceptionally warm because heat stored in the tropical Pacific ocean is released to the atmosphere. The previous warmest month was in August 2016 at the end of a very strong El Niño event. There was a weak El Niño this winter and spring that has already faded to neutral, an event that wouldn’t be expected to cause record summer heat in the northern hemisphere. However, global sea ice extent dropped to a record low in late April and has remained at record low levels through mid-August. This has reduced the reflection of light and heat back to space by ice, adding heat to the polar oceans and seas.
Record low sea ice extent in July led to an extraordinary build up of heat in the Arctic ocean and Arctic seas because heat was taken up by dark open water instead of reflected back into space.
The elephant in the room that has not been discussed by the media about this summer’s extraordinary northern hemisphere heat is the atmospheric circulation pattern. As far as I have been able to determine from reviewing climate data center maps of the atmospheric circulation over the polar region, there has been unprecedented subsidence from the stratosphere into the polar region causing unprecedented heat in the lower atmosphere over the Arctic. One of the predicted consequences of increasing greenhouse gas emissions is an intensification of the atmospheric circulation up to and down from the stratosphere. It’s called the Brewer Dobson circulation and it’s intensification appears to be amplifying Arctic warming this summer.
Record heat, unprecedented Siberian fires, record low sea ice extent and accelerating degradation of permafrost are speeding up the impacts of human greenhouse gas emissions and deforestation. Moreover, there’s inertia in surface temperatures caused by the mixing of cold ocean water stored when the climate was cooler. We’re rapidly approaching the IPCC limits of 1.5 C and 2.0 C after which increasingly catastrophic effects of climate change can be expected. The feedback loops are already having impacts. Every delay to action to cut GHG emissions and deforestation will be amplified by natural processes. This summer foreshadows the future.