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Globally decreasing bird numbers – Part 1: Climate

Barry Muir | Guest contributor

Numbers of birds are decreasing globally (Lees et al. 2022). Approximately 48% of existing bird species worldwide are known or suspected to be undergoing population declines. Populations are stable for only 39% of species. Only 6% are showing increasing population trends, and the status of the other 7% is still unknown.

The study authors (Lees ibid.) from England, USA, Birdlife International, South Africa, Italy, and the Nature Conservation Foundation, reviewed changes in avian biodiversity using data from the International Union for Conservation of Nature (IUCN)’s Red List to reveal population changes among the globe’s 11,000 bird species. A similar decline has been found in urban Australia (Mamac 2022 – partly based on BirdLife Australia’s Birdata), and, although the primary causes are land clearing, hunting and urbanisation, climate change and alteration of fungal and insect populations are key factors in the loss of birds.

If we are going to consider climate change as a factor in bird population decline, we must first be convinced that climate change is real. There are many sceptics who suggest that climate change is the construct of scientists and politicians for their own ends.

Myth 1

The first myth in this regard is the often-expressed opinion that there are only a few people who believe climate change is real and that it is a very recent idea. The graph below might help to dispel that opinion.

Graph 1: Scientific agreement on human-caused global warming. Modfied from Verheggen B (2016)

Note 1: Callendar G S. (1938). The artificial production of carbon dioxide and its influence on temperature. Quarterly J. Royal Meteorological Society. 64 (275):223–240.

Note 2: Tyndall J. (1860). Note on the transmission of radiant heat through gaseous bodies. Proc. Royal Society of London. The Royal Society. 10:37–39.

I won’t bore you with the science of Tyndall’s work in 1859 and published in 1860, but it is pretty clear that the concept of climate warming is not a new idea. Further, it is highly unlikely that almost 15,000 signatories to the 2022 World Scientists Warning on the Climate Change Emergency are all in cahoots for their own gain!

Myth 2

The second myth is that the climate has changed before and so this is nothing new. Yes, there have been Ice Ages and periods of warming, but what is happening now?

Graph 2 below is informative because it shows global air temperature anomalies (i.e., variations above or below long-term average) since 1850. Prior to about the 1980s there were peaks of high temperature – one in the late 1870s killed 50 million people in south Asia. This was the result of extremely unusual climate conditions which I won’t go into here.

Graph 2 shows that global temperatures began to rise steadily after about 1910 when industrialisation and use of motor vehicles went rampant. The next highest peak was during the Second World War when fires and the machines of war produced a vast amount of heat and carbon dioxide.

However, these events pale into insignificance compared with temperature rise since about the 1980s. It is also noteworthy that in 1850 the global population was about 1.3 billion people whereas now it is over eight billion people – any changes to global environment will have a much greater effect than previously.

Graph 2: Global air temperature anomalies (above or below long-term mean) since 1850. Source:

Myth 3

The third myth is that global air temperatures vary from one place to another, so each data set is unreliable. Yes, they do vary from one place to another, so one must look at temperatures from several sources. Graph 3 is helpful because it shows data from five independent sources spread around the globe. They all record a significant rise in temperature.

Graph 3: Global average temperature change from five independent sources.

So, the real issues are:

(a) that global climate change is occurring (regardless of the cause) and humanity is not prepared for it;

(b) the rate of change which has occurred over the last 100 years in particular, and which may have previously occurred over thousands of years, is now rapid. There is little time for humans, animals, fungi or plants to adapt; and

(c) there are now over eight billion people swarming over the planet. At the time of the last major global warming event (about 50,000 years ago) humans were few in number, living in primitive circumstances, and able to readily migrate if climate and food availability became untenable. That situation no longer exists.

The argument that Australia contributes such a small amount, to global carbon dioxide emissions, that we don’t need to worry is basically true. Australia only produces about 1.1% of global greenhouse emissions compared, for example, with (November 2023 Visual Capitalist data) China (30.9%); USA (13.5%); or India (7.3%), but that is not the point.

The fact that we (Australia) are only a small producer does not justify increasing our emissions unnecessarily, such as by actively promoting coal production as a major fuel. It also gives us the opportunity to make strong policies that may encourage others on the world stage to think more closely about what they are doing. After all, their poor decisions and lack of action will damage Australia as much, or perhaps more, than it will affect their own countries. By not “walking the talk”, we send a message of insincerity and tacit support for their dangerous policies.

Having provided that background, in the next article I will look at climate change affecting fungi and how that, in turn is affecting bird populations.

Further reading

Ripple WJ et al. (11 others) (2022). World Scientists’ Warning of a Climate Emergency 2022. BioScience 72: 1149–1155.


Lees AC et al. (8 others) (2022). State of the World's Birds. Annual Review of Environment and Resources 2022; 47(1). Doi: 10.1146/annurev-environ-112420-014642

Mamac M. (2022). Why Aussies are seeing fewer backyard birds. Asian Scientist August 25, 2022


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