Global temperature is affected by a lot of things, not just humans and their greenhouse gases. We know what some of those things are, and we can even estimate their impact over the last 40 years or so (since 1979 let’s say). Then we can subtract that effect from temperature data, to estimate how hot Earth would have been without those “other things.”
What other things, you wonder? Known factors include the El Niño Southern Oscillation (ENSO), volcanic eruptions, and variations in the output of the sun; published research outlines the method I used (although I’ve tweaked it a bit). Let’s take, for instance, the global temperature from NASA (monthly averages from January 1979 through December 2019):
I recently looked for trends in precipitation in New South Wales, searching for a regional rather than continental trend. There wasn’t much to find, no real evidence of change in the yearly average rainfall. But we can also look for trends on a seasonal rather than annual basis, and we can do so for all seven Australian states for which the BoM kindly provides precipitation data.
When we isolate seasons, we find some patterns strong enough to rise above the noise. For example, Victoria has been getting dryer during Autumn:
In recent posts I’ve featured graphs of the average daily high temperature in Australia during summer. Here’s one of temperature throughout the entire year; black dots show each year’s average, while the red line with pink shading around it shows an estimate of the trend and its uncertainty range (just an estimate, mind you, but it’s based on math, not on “looks like”)
The trend line emphasizes two things Australians need to know:
1: The trend is going up — overall, Australia is hotter than it used to be and getting hotter.
2: Temperature doesn’t just follow the trend. In addition to its “overall” pattern it also fluctuates, incessantly.
Some people have wondered about the trend in Australia’s summertime daily high temperatures.
The last post discussed Australia’s hottest summer (the latest) and Jennifer Marohasy’s attempt to pervert the truth. But I didn’t talk about the trend, which must have surprised regular readers because I tend to emphasize that. A lot. I did show this graph:
One of the things making wildfire/bushfire worse, contributing to the current conflagration in Australia, is the increase of daily high temperatures. It increases the Vapor Pressure Deficit (VPD), the difference between how much water vapor the air can hold and how much it does hold. When VPD is high, it can suck the moisture right out of potential fuels big and small, which increases the frequency and severity of fire dramatically.
The data are clear, that for daily high temperature last year (2019) was the hottest on record for Australia:
A reader asked that I estimate the trend in the JRA-55 data for global temperature, because it is touted by climate deniers Patrick Michaels and Ryan Maue. Let’s have a look. Here’s the data:
Comments on the last post speculated that rainfall in Australia might show a trend if one looked at smaller regions than the entire continent. In particular, some wondered about the history of precipitation in New South Wales (NSW, one of the areas hardest hit by bushfires), and one reader was kind enough to point to data from Australia’s BoM (Bureau of Meteorology), featuring this map of the trends in rainfall since 1970 throughout NSW:
Almost every part of the state shows a declining trend. But how significant is the trend?