As heatwaves swept through Australia’s southeast this week, we’ve been updating Australia’s climate stripes, also known as warming stripes.
How to read climate stripes
Climate stripes are minimalist by design. Their purpose is to tell a story about long-term trends, not datapoint details.
Each stripe shows the difference in temperature from a baseline average. That is, the size of the anomaly. (That begs the question, what’s the baseline average? It’s complicated and there’s more on that below. But these charts use the 30-year period between 1961 and 1990).
Climate Stripes are powerful because they show patterns. One record-hot day might make headlines, but it won’t affect the stripes. Frequency of days that are hotter-than-average is what makes the columns of red grow and pop.
National picture: Australia to end of August
Australia’s average maximum temperature in August was 3.09°C above average. It was the second-warmest August on record.
If we put every month since 1910 in a list and order them by extremity of anomaly (hot to cold), August 2023 was ranked 8 out of 1364.
The stripes below show the average monthly maximum temperature in Australia for each month since January 1910.
Winter in the eastern states
Australia recorded its warmest winter since national observations began in 1910. It was most extreme in Queensland, NSW and Tasmania.
Collectively, the average maximum temperature in Australia’s eastern states was 2.29°C above average – the highest on record.
The stripes below show the average maximum temperature during winter in Australia's eastern states for every winter since 1910.
September in Sydney
This week, a heat wave swept across parts of Australia’s south-east.
Sydney’s average maximum temperature for the month of September is 20.4°C (using the 1961-1990 baseline).
The stripes below show the daily maximum temperature for every September day since 1910 to 20 September 2023.
The bright red line on the far right was the last week. It’s an intense colour because there were consecutive days of extreme anomalies.
From Saturday to Wednesday, temperatures exceeded the average by 11.4°C, 12.4°C, 9.4°C, 14.2°C and 13.5 °C.
It’s warmer than average. But what’s average?
The World Meteorological Organisation (WMO) sets standard reference periods to be used as international baselines. This helps bring consistency to global climate monitoring and analytics.
The reference periods are 30 years long to smooth out natural climate variability.
Not all reference periods are frozen in time. In a post published by the UK's Met Office, WMO scientists said data used for operational decision-making (such as predicting peak energy load or crop planting times) should use the most recent reference period, which is updated every decade.
But the WMO says long-term climate change monitoring should use a fixed historical reference period as the benchmark. The WMO Reference Period for long-term climate change assessment is based on the period 1961-1990.