As noted by a recent report by the World Meteorological Society (and many other news articles), July of 2018 has brought exceptionally warm air temperatures to many parts of the globe. Fires rage in Sweden and Greece, Japan experienced deadly torrential rains (1,800 mm at Shikoku) followed by temperatures reaching 106°F. In Algeria, Ouargla reported a maximum temperature of 124.3°F and Morocco set a new record at Bourfa at 110°F. In Canada, as many as 70 people may have died due to an extreme heat wave in Quebec. Closer to home, the WMO report identifies an extreme of 125.6°F in Death Valley, while Chino, Burbank and Van Nuys set records at 120°F, 114°F and 117°F.
This blog posting is not intended to provide a formal climate attribution analysis, such as those provided by the Bulletin of American Meteorological Society. The goal here is just to look at the data, which is quite compelling on its own. We begin by looking at annual (July to June) air temperatures for Coastal Southern California (Figure 1). This data was obtained from the Earth Systems Research Laboratory. What is very concerning about this time series is how every year since 2014 has been very warm. I’ve circled these values. This type of persistent warmth can dry out vegetation and provide great background conditions for fires.
We can present the same data as five-year averages to highlight the recent transition to warmer conditions (Figure 2). Now the past five-year average clearly stands out as way warmer than any value on record before 2013. The current five-year average temperature (~52.8°F) is about two degrees Fahrenheit warmer than the average from just a few years ago. This is a large change in a short period of time. Beginning with the last El Niño in 2014/16, we may have transitioned to a much warmer climate regime, and climate model projections indicate that this warming will continue. I have also plotted similar results for Central California where the Ferguson fire rages (Figure 3). We have seen an historically unprecedented and very rapid increase in air temperatures. Currently, about 20 fires are burning in California, and 2017 was clearly the most destructive fire year on record. While warm temperatures are just part of the recipe for fire disasters, this part of the puzzle has clearly been expanding rapidly.
If we produce a similar plot of GLOBAL five-year average air temperature anomalies, based on NASA estimates of land surface temperatures (Figure 4), we see that global temperatures have also jumped upwards over the past five years, reaching unprecedented heights. The magnitude of the jump in coastal (Figure 2) and central (Figure 3) California has been substantially greater in magnitude, however. Also shown in Figure 4 are completely independent predictions of global land air temperature anomalies based on the current state of the science collection of climate change simulations. The fit to the observations is extremely good (R2=0.97). Climate change has caused the recent increase in global temperatures.
The rise after 2018 is based on a pessimistic but realistic ‘business as usual’ climate change scenario in which the climate modelers have assumed a continued rapid increase in greenhouse gasses. I have annotated this time series with 10 year steps to emphasize what we may likely experience between 2019 and 2048. Between 2009 and 2018, we have already seen a problematic increase in global and California air temperatures related to numerous climatic hazards. Without dramatic efforts to reduce our greenhouse gas emissions, the models (which have been extremely accurate so far) tell us that we are likely to experience three more similar increases between now and mid-century. For poor people living in very warm regions (like India), such warming may lead to severe health impacts as described by Somini Sengupta. For California, a further intensification of droughts and fire risk seems likely as temperatures continue to increase rapidly.
To visualize US temperature changes, we can use the cool ‘Climate Explorer’ website provided as part of the U.S. Climate Resilience toolkit. If you click HERE you should get a map of the continental U.S. that shows the number of days in a year with maximum air temperatures of greater than 95°F. The map is divided with a vertical bar identified with left-right arrows (<>). On the left hand side of the bar is a map of recent counts based on 1961-1990 observations. On the right is a map of estimates for 2090 based on a continued higher emissions trajectory. Grab the central bar and slide it back and forth, and you can see the predicted change – big increases in the frequency of very warm days.
We can also use the Climate Explorer to examine likely changes in a given location – like Santa Barbara county (HERE). This time series contrasts likely outcomes given a continuation of our current high emission pathway (shown in pink and red) and likely outcomes if we act to curb emissions (blue). As you can see, there is substantial uncertainty, but we see a substantial difference between the scenario averages (red and blue lines) by mid-century. If we do not curb emissions soon, by 2100 the models suggest that we could very well see annual average maximum temperatures increase by ~+7.3°F, according to the ensemble average.