Climate change hot issue

FACT: HUMANS ARE TO BLAME FOR WORSENING WEATHER PATTERNS

A warmer atmosphere and oceans are causing dramatic changes.

It is proven that humans are the overwhelming cause of the long-term changes in the climate that we are observing. Despite this, climate denialists continue to receive prominence in some media, which can lead people into thinking that man-made climate change is still in question. So it’s worth going back over the science to remind ourselves how much has already been established.

Successive reports by the Intergovernmental Panel on Climate Change – mandated by the United Nations to assess scientific evidence on climate change – have evaluated the causes of climate change. The most recent report on global warming of 1.50C confirms that the observed changes in global and regional climate over the past 50 years are almost entirely due to human influence, not natural causes.

First, what do we mean by climate change? The panel defines it as “a change in the state of the climate that can be identified by changes in the mean and/or the variability of its properties and that persists for an extended period, typically decades or longer.”

The causes of climate change can be any combination of:

Internal variability in the climate system, when various components of the climate system – like the atmosphere and ocean – vary on their own to cause fluctuations in climatic conditions, such as temperature or rainfall. These internally-driven changes generally happen over decades or longer; shorter variations such as those related to El Nino fall in the bracket of climate variability, not climate change;

Natural external causes such as increases or decreases in volcanic activity or solar radiation. For example, every 11 years or so, the sun’s magnetic field completely flips and this can cause small fluctuations in global temperature, up to about 0.20C. On longer time scales – tens to hundreds of millions of years – geological processes can drive changes in the climate, due to shifting continents and mountain building; and

Human influence through greenhouse gases (gases that trap heat in the atmosphere such as carbon dioxide and methane), other particles released into the air (which absorb or reflect sunlight such as soot and aerosols) and land-use change (which are fossil fuel burning, cement production, land cover change (especially deforestation) and agriculture.

Most of us will struggle to pick up slow changes in the climate. We feel climate change largely through how it affects weather from day to day, season to season and year to year.

The weather we experience arises from dynamic processes in the atmosphere, and interactions between the atmosphere, the oceans and the land surface.

Human influence on the broader climate system acts on these processes so that the weather today is different in many ways from how it would have been.

One way we can more clearly see climate change is by looking at severe weather events.

A branch of climate science, called extreme event or weather attribution, looks at memorable weather events and estimates the extent of human influence on the severity of these events.

It uses weather models run with and without measured greenhouse gases to estimate how individual weather events would have been different in a world without climate change.

As of early this year, nearly 70% of weather events that have been assessed in this way were shown to have had their likelihood and/ or magnitude increased by human influence on climate.

In a world without global warming, these events would have been less severe.

About 10% of the studies showed a reduction in likelihood, while for the remaining 20%, global warming has not had a discernible effect.

For example, one study showed that human influence on climate had increased the likelihood of the 2015-2018 drought that afflicted Cape Town by a factor of three.

Weather extremes underlie many of the hazards that damage society and the natural environment we depend upon. As global warming has progressed, so have the frequency and intensity of these hazards, and the damage they cause.

Minimising the impacts of these hazards, and having mechanisms in place to recover quickly from the impacts, is the aim of climate adaptation, as recently reported by the Global Commission on Adaptation.

As the commission explains, investing in adaptation makes sense from economic, social and ethical perspectives.

And, as we know that climate change is caused by humans, society cannot use “lack of evidence” on its cause as an excuse for inaction any more.

Human influence had increased likelihood of drought

Mark New is director of African Climate and Development Initiative at the University of Cape Town.

Republished from TheConversation.com