Here’s the background to one of the most commonly used phrases in news – climate change. We’ll steer clear of the politics and rather take you through what climate change means, why it’s a problem, what the world has agreed to do about it, and Australia’s position.

KNOW YOUR CLIMATE
How does the climate work?
Energy from the Sun is the key determinant of how our climate works. A good part of that energy is deflected back into space by Earth’s atmosphere, the clouds, and land, ice and water surfaces. A lot of that energy is absorbed and most of it is returned to into space as heat. And then some of that heat is captured by gases in the atmosphere by what’s called ‘greenhouse gases’. We’re talking about gases like carbon dioxide, methane and water vapour. They re-radiate that energy downward to Earth – which is something called the ‘greenhouse effect’. Without the greenhouse effect, earth would be 33C cooler – so it makes earth habitable. 

What is climate change?
At its broadest definition, climate change is a change in the pattern of weather, and related changes in oceans, land surfaces and ice sheets, occurring over time scales of decades or longer. So we’re not talking about one hot summer or blips in ocean temperatures, we’re talking about longer term trends, and scientists usually like to get a look across at least 30 years of data. 

What causes climate change?
There’s a couple of things to point to here. 

1. Climate change may be due to natural processes. Things like changes in the Sun’s radiation, volcanoes – natural occurrences that are out of our control. 

2. It can also be a result of human influences such as changes in the composition of the atmosphere where the balance of those greenhouse gases change significantly. It can also be things like significant land use changes – and that’s why the Amazon rainforest fires has been in the news this year. 

SO WHAT’S HAPPENING?
Where do we start?

Ever since there’s been an Earth (and we’re talking 4.5 billion years ago that it was formed), there’s been climate change. There’s been times when the Earth has been much cooler, and much warmer than it is now. And while there have been some variations, our climate has been relatively stable for the last 8,000 years. 

So what’s changed?
The industrial age is reponsible for the change. Since the 19th century, human-induced carbon dioxide emissions from fossil fuel combustion, cement manufacture and deforestation have disturbed the balance, adding CO2 to the atmosphere faster than it can be taken up by the land biosphere and the oceans.

What’s that led to?
Between 1850 and 2012, globally averaged near-surface air temperature rose by around 0.8C. Warming from pre-industrial levels to the decade 2006–2015 is assessed closer to 0.9°C. The increase in temperature quickened from the 1970s, and that’s a trend that’s continuing. The data says that the last decade has been the warmest decade since the 1850s. 

Our oceans are also warming. It’s an interesting fact to note – more than 90% of the total heat accumulated in our climate system between 1971 and 2010 has been stored in the world’s oceans. 

Here in Australia, the average surface temperatures over the Australian continent and its surrounding oceans have increased by nearly 1C since the beginning of the 20th century. Seven of the 10 warmest years on record in Australia have occurred since 2002.

What effect could climate change have?
It has the potential to touch about everything – human health, agriculture and food security, water supply, energy production, the environment and diverse plant and animal ecosystems, and many many others.

WHAT’S THE WORLD DOING ABOUT IT?
The Paris Climate Agreement
It’s central aim is to strengthen the global response to the threat of climate change. The agreement – to keeping the global temperature rise this century well below 2C above pre-industrial levels and to pursue efforts to limit the temperature increase even further to 1.5C. It was agreed in 2015, came into force in 2016, and there are currently 185 countries who are signatories to the agreement, including Australia, who all together make up the vast majority of the world’s emissions. 

Who didn’t sign?
Pretty much everyone has. Even Syria… The notable point is US President Donald Trump has said the US will pull out of the agreement as soon as it can, which will be in late 2020. The US is responsible for about 18% of the world’s greenhouse gas emissions. 

What is Australia’s plan?
To meet our Paris obligations, it’s the Coalition Government policy to reduce emissions to 26-28% on 2005 levels by 2030. In broad terms, they’re doing that through a mix of policies on upping renewable energy output, improve energy productivity, investing in clean technology, and funding agencies like the Clean Energy Finance Corporation, the Australian Renewable Energy Agency and the Clean Energy Regulator to make it work. In total, the budget allocation for climate change related initiatives from FY20 for the coming four years is $6.25 billion. 

IF THAT’S ALL SETTLED, WHAT ARE PEOPLE STILL TALKING ABOUT?
Well, science is never completely settled. As a relatively newly emerging field of scientific study, there’s been a lot of conjecture about the data and its findings. The particular sticking points have been:

• Have humans really impacted climate change?

• And if so, by how much?

Some remain sceptical, but just this year there seems to be broader agreement in the wider scientific community, including by our CSIRO, that the findings about human-related global warming are robust. One number that was doing the rounds recently – the scientific consensus that humans are causing global warming is likely to have passed 99%. 

What else?
Those who want to see more action on climate change are focused on:

• Encouraging nations to move more quickly to reduce their carbon emissions. 

• Take further steps to mitigate for a 1.5-2C rise in global temperatures. 

Who is leading the charge?
The United Nations continues to take a lead on building momentum for action on climate change. They will hold two big summits in the second half of 2019 and beyond to; “showcase a leap in collective national political ambition and it will demonstrate massive movements in the real economy in support of the agenda. Together, these developments will send strong market and political signals and inject momentum in the “race to the top” among countries, companies, cities and civil society that is needed to achieve the objectives of the Paris Agreement and the Sustainable Development Goals.”