July and August are typically about 3.6ºC or 6.5ºF warmer than December and January. August is typically 1.8°C or 3.24ºF warmer than the average annual temperature. Above image shows how much higher the temperature was for selected months, compared to the annual global mean for the period 1980-2015. Will August 2018 be the hottest month on record?
Numerous temperature records have fallen across the world recently. Heat stress hazard is high under conditions of high surface air temperature and high relative humidity. When looking at heat stress hazards, it's therefore important to look at surface air temperatures over land, i.e. the temperature of the air above the land surface.
Fire hazard is high under conditions of hot and dry soil and strong wind. When looking at fire hazards, it's therefore important to look at land surface temperatures, reflecting how hot the surface of the Earth would feel to touch in a particular location. The map below shows land surface temperatures.
When calculating how much warmer it is now, a number of things must be taken into account:
What baseline is used and how is the temperature at the baseline calculated? In the image at the top, the baseline is 1980-2015, which is a very recent period. When using a preindustrial baseline, anomalies could be more than 0.6°C higher than when using the 1951-1980 baseline that NASA normally uses.
- Surface temperatures or surface air temperatures?
Above map shows land surface temperatures. As said above, this is different from surface air temperatures over land that show the temperature of the air above the land surface.
Similarly, sea surface temperatures indicate the temperature of the water at the surface. Sea surface air temperatures, on the other hand, are slightly higher, they are measurements of the air temperature just above the surface of the water.
NASA typically uses surface air temperatures over land, while using surface water temperatures over oceans. When instead using air temperatures globally, the temperature anomaly could be more than 0.1°C higher.
- Missing data
How are missing data dealt with? To calculate the global mean on maps, NASA uses four zonal regions (90-24ºS, 24-0ºS, 0-24ºN, and 24-90ºN) and fills gaps in a region by the mean over the available data in that region. In datasets, however, missing data are typically ignored. This could make a difference of 0.2°C. Ignoring data for the Arctic alone could make a difference of 0.1°C.
BTW, remember the Paris Agreement, when politicians pledged to take efforts to ensure that the temperature would not cross 1.5°C above preindustrial?
The situation is dire and calls for comprehensive and effective action, as described in the Climate Plan.
• The Northwest is Running Hot and Dry
• NASA GISS (Goddard Institute for Space Studies) Surface Temperature Analysis (GISTEMP)
• How much warming have humans caused?
• How much warmer is it now?
• Climate Plan