Source: Channel News Asia 
Date: 3 August 2020

The Australian bushfires from September last year to early February are proof to many people that man-made or "anthropogenic" climate change is real and threatening.

But for some Australians involved in the coal-mining industry, the fires seemed to mainly be a natural catastrophe: Australia has had bushfires, even serious ones, since time immemorial and so there is no reason to put the blame on the exploitation of fossil fuels.

So, is anthropogenic climate change real? Or is it be a matter of personal opinion?

Scientists say Australia's fire seasons are beginning earlier and burning with more ferocious intensity due to climate change. (Photo: AFP/Saeed Khan)

Big History of Climate Change

Let us start with a simpler question: has the climate really changed?

The weather varies from day to day and season to season. These changes tend to reverse so that the environment never strays far from a stable, mean condition. This stable condition is what we refer to conceptually as the climate.

Climate refers to both the physical and chemical state of the environment. It characterises not just the air but also the land, sea and ice on the planet. Therefore, a change in climate is a fundamental shift in the environment, unlike changes in weather, which is shorter term.

Since the late 19th century, instruments documenting the average temperature of the Earth's surface show that the temperature has gone up by about 1 degree Celsius.

Over the same period, the global mean sea level has climbed by nearly one-quarter metre at an increasing pace. This is because oceans expand thermally and because ice-caps and glaciers melt and flow into the sea.

The chemical composition of the air is also a telling marker for our changing climate: carbon dioxide concentration has risen from around 290 ppmv (parts per million by volume) in 1880 to 400 ppmv in 2020.

Today's elevated level of carbon dioxide is alarming because ancient air bubbles trapped in Antarctica's ice reveal that the level never exceeded 300 ppmv for the past 800,000 years. The big history of climate change has arrived.

How Does Climate Change Affect Us?

When the climate warms, extreme hot, dry weather becomes more severe and last longer, thus increasing the occurrence of forest fires that destroy life and property. This is what happened in Australia's case.

A view of Singapore's skyline around Marina Bay on Sep 23, 2019, amid the ongoing haze.

Smoke from widespread fires creates haze which irritates the eyes and exacerbates respiratory illnesses. A regional haze episode can last for weeks to months.

Meanwhile, unreliable water supply from rain catchment compels cities to rely more on costly desalination and water reclamation technologies. Just recall the dry spell in Singapore from July to September last year.

As the sea level rises, agriculture in low-lying river deltas takes a hit: the Mekong delta has suffered from seawater seeping into precious paddy fields.

As food prices tend to rise whenever food production falls, a populous, rice-importing nation like Indonesia is vulnerable to rice production cut-backs in Vietnam.

There are many other examples that illustrate how climate change impacts negatively our lives and the economy. But the consequences go beyond human society as ecosystems are sensitive to environmental changes too.

Warmer seas have bleached coral from the Great Barrier Reef in Southwest Pacific to the Maldives in Indian Ocean, for instance.

Understanding the Root Cause

Nowadays, many climate change sceptics no longer deny the reality of climate change. However, they argue that climate change is due to natural causes like an increase in the Sun's radiation.

So how do we know that the scientists are right when they say that climate change is mainly caused by emissions of greenhouse gases?

Greenhouse gas emissions are now the fastest-growing contributor to ecological overshoot. (Photo: AFP)

The science of how greenhouse gases lead to global warming is no mystery: a greenhouse gas (GHG) is an atmospheric constituent that is effective in absorbing and emitting infrared radiation - a kind of light that has a longer wavelength than is visible to our eyes.

Water vapour, carbon dioxide and methane are the three most abundant naturally occurring GHGs. The Earth's surface emits mainly infrared light upwards which is mostly absorbed by GHGs.

Then GHGs re-emit the infrared light, some eventually escaping upward into space while the rest goes back downward. The Earth's surface re-absorbs the downward infrared light converting some of it into heat.

This radiative transfer naturally keeps the Earth warm enough for life to exist.

But from the time of the industrialisation, humankind has burnt much coal, oil and natural gas for energy, producing excessive carbon dioxide that has accumulated to the unprecedented levels today.

Fossil-fuel mining, cattle farming and rice cultivation have also released much methane into the environment. The increased concentration of GHGs leads to greater absorption and re-emission of infrared light, causing the Earth's surface to be excessively warm and hence the sea level to rise.

People take part in protests ahead of the upcoming G20 summit in Hamburg, Germany July 2, 2017. Placard reads "Global Warming is NOT a Myth". (Photo: REUTERS/Hannibal Hanschke)

Refuting the Climate Sceptics

There is an important fact which refutes the sceptics' argument that the Sun's radiation has simply increased.

It is a little known fact that the temperature of the atmosphere does not change uniformly.

Observations made by satellites from space show that around 15 to 25 km above the Earth's surface, in a layer of the atmosphere called the "lower stratosphere", there has been a long-term cooling trend since the late 1970s.

The existence of global cooling refutes the climate sceptics' simple explanation that today's climate change is due to the Sun warming the Earth more. At the same time, this reinforces our understanding of the GHGs' effect.

The sun sets behind an oil pump outside Saint-Fiacre, near Paris, France September 17, 2019. (Photo: REUTERS/Christian Hartmann)

When GHGs absorb infrared light, they re-emit the radiation both downwards and upwards. As the downward infrared light warms up the Earth's surface, the upward infrared light simultaneously carries energy away into space.

It is the increase in escaping energy from higher GHG concentration that cools the lower stratosphere. The distinctive pattern of warming-below-and-cooling-above is the fingerprint that identifies the culpability of GHGs.

Fast-forward to the Future

The climate has been changing for more than 100 years because of man-made GHG emissions.

Projecting into the future, if we continue our business as usual, carbon dioxide levels are expected to exceed 900 ppmv before the year 2100.

Scientists estimate that global average surface temperature will warm by about 3 to 5 degrees Celsius and global mean sea level will rise by about half to one metre over the 21st century. Changes in rainfall patterns are harder to predict but in Southeast Asia, droughts will likely worsen.

Person with an umbrella during a spell of hot weather in Singapore. (Photo: Gaya Chandramohan)

Today, Singapore's daily temperature varies on average between 25 and 31 degrees Celsius. This spans 6 degrees Celsius.

If we fast-forward to the decade 2091 – 2100, Singapore may be confronted with the possibility that its normal night-time temperature would be as high as today's normal day-time temperature!

By 2100, about half the land in the Mekong delta of Vietnam could be lost to seawater intrusion. The risks posed to water and food resources will be grave if we continue to emit GHGs while ignoring climate change.

Act Today, Live Better Tomorrow

The anticipation of dire consequences of anthropogenic climate change in the lifetimes of our children and grandchildren should spur us into action today in reducing GHG emissions and adapting to climate change.

There are four sets of actions that individuals can resolve to:

One, to conserve energy because most fossil fuel today is burnt to provide energy. For example, enjoying fewer hot showers and raising temperature settings in air-conditioners, or using more public transport and taking the stairs instead of the lift, all contribute to mitigate the emissions of carbon dioxide.

Two, to save water and reduce food wastage. The purification or reclamation of freshwater and the production, processing and transport of food expends energy, indirectly emitting carbon dioxide.

Moreover, when food supply matches closely food demand, less methane is released unnecessarily in food production.

Three, to avoid the use of plastics whenever possible. Plastics are mainly manufactured from petrochemicals derived from crude oil. When incinerated after disposal, plastics convert to carbon dioxide too.

Four, to pay attention to and pick out scientifically reliable information on climate change. This would foster an enlightened and responsible attitude in supporting climate action policies.

While the above actions are not going to stop climate change, because the current-day elevated levels of GHGs are already warming the Earth's surface, they help to alleviate future impacts and ease adaptation to the new climate.

Anthropogenic climate change is real. We have to act now.

Written by Associate Professor Koh Tieh Yong, a climate scientist at the Singapore University of Social Sciences.