Weather is what we experience every day and every hour — even, sometimes, from minute to minute — and it varies depending on where we are. Climate, on the other hand, tracks long-term trends such as changes in mean global surface temperatures over decades, centuries and longer periods.
For example, Earth’s climate is influenced by its orbital path around the sun, which changes on a roughly 100,000-year cycle. It is also influenced over shorter cycles by changes in Earth’s tilt and precession.
The roughly 100,000-year cycle helps account for major swings in mean global temperatures between glacial and interglacial periods. The latter are associated with higher ocean levels, warmer temperatures, lakes and rivers and often abundant vegetation and other life. During glacial periods, ocean levels drop and, at higher latitudes such as western Europe during the last ice age, life for humans and Neanderthals was much tougher.
These swings between interglacial and glacial periods are reflected in changes in mean global temperatures.
Earth’s climate is influenced by the relatively short wavelengths of incoming light energy from the sun. That energy is absorbed by Earth and radiated back into space at longer wavelengths, as infrared radiation. Some of that outgoing energy is absorbed by greenhouse gases such as water vapour, methane and carbon dioxide.
Methane and carbon dioxide, unlike water vapour, can remain in the atmosphere for much longer periods. Historically, their concentrations were relatively small and the amount of outgoing heat energy shed into space more or less balanced the incoming energy from the sun.
The problem arose as levels of greenhouse gases such as carbon dioxide increased to the point that more outgoing energy became trapped in the atmosphere. The result is an increase in temperatures in both the atmosphere and on Earth’s surface.
The world’s oceans act like a huge heat sink, able to absorb and buffer much of that additional heat — but only to a point. As they absorb more heat, ocean temperatures increase, especially near the surface.
Making matters worse, a hotter atmosphere can hold more water vapour and therefore more heat, aggravating the warming problem.
The central villain in this climate tragedy is carbon dioxide generated by the burning of fossil fuels. Sophisticated climate models make that clear despite the claims of climate change deniers.
It was one reason the Nobel committee in 2021 stepped beyond its usual cautious role by emphasizing the strength of the scientific evidence for global warming and raising the alarm about what could happen if mean global temperatures continued to rise much beyond one to two degrees Celsius.
Beyond certain thresholds, warming can trigger feedback effects that contribute to still greater temperature increases and more severe effects on climate and weather.
Looking back, mean global temperatures began to climb around the middle of the last century and have risen much faster so far this century, alongside the worldwide use of fossil fuels.
Unfortunately, Earth remains on track for much higher temperatures because accumulating carbon dioxide can trap additional heat in the atmosphere for a long time, with no quick way to reverse the trend.
Making matters worse are predictions that the coming El Niño event could be among the strongest in centuries, supercharged by a band of unusually warm tropical water in the central Pacific moving toward South America. It could bring large areas of heavy rainfall or drought this fall and next year, depending on the region, while adding to already high global temperatures driven by greenhouse gas emissions.
If all that sounds like a recipe for disaster, it surely is.
We have witnessed the effects of rising mean global temperatures in recent summers, evident in the widespread destruction of forests by wildfires in North America and Europe, record-breaking summer temperatures, extreme rainfall and flooding and, elsewhere, severe drought in places where seasonal rains would normally be expected, including parts of India.
What can be done?
The science behind climate change and its principal culprit — rising greenhouse gas emissions generated primarily by burning fossil fuels — has been clear for decades.
However, building a consensus strong enough to bring all of the world’s countries together has proven impossible in the present political climate.
The same stubborn reluctance to resolve ongoing conflicts in the Middle East and elsewhere reveals humanity’s fatal weakness: the innate tribalism that divides people, even in the face of major tragedies such as those in Sudan, Gaza, Lebanon, Israel and Iran.
Need I go on?
I don’t know what the answer is, or whether any solution is even possible at this stage, but the outcome where climate change is concerned seems certain.
Far worse weather is in store in the coming decades, with no solution in sight.
Dr. William Brown is a professor of neurology at McMaster University and co-founder of the InfoHealth series at the Niagara-on-the-Lake Public Library.
