What is climate change?

To understand why transitioning to a low-emissions Aotearoa is necessary, it can help to understand the basics of climate change.

Aotearoa has committed to reaching net zero emissions of long-lived greenhouse gases by 2050 and reducing biogenic methane emissions between 24-47% by 2050. But what are greenhouse gases and why do they matter? How is climate change affecting us? 

In order to understand why it is so important for Aotearoa to act on climate change, it can be helpful to understand the basic foundations of climate change. Below are a series of questions we get asked regularly. You can also find more information on the Ministry for the Environment website.

What are greenhouse gases, and why do they damage the planet? 

Scientists have understood the role of greenhouse gases in global climate systems for more than 160 years. The sun’s energy warms the earth’s surface, oceans, and atmosphere, and greenhouse gases trap this warmth to make life on earth possible – a similar role to glass in a greenhouse, which is where the name comes from. Without them, the average temperature of the earth would be around -18°C.  The most important greenhouse gases are carbon dioxide, methane and nitrous oxide.

These greenhouse gases occur naturally, and if natural processes were the only source of these gases, the world’s climate would be stable, or only warming or cooling very slightly.  However, following the Industrial Revolution where fossil fuels started to play a central role in powering machines and production processes, human activity has created additional sources of these gases, increasing the volume being released into the atmosphere. These extra greenhouse gases trap more of the warmth than would occur naturally. This greater warming effect is driving what is commonly referred to as ‘climate change’.

Why, and how much, will the climate change?

Greenhouse gases from human activities are building up in the atmosphere and making our climate warmer and warmer. Research can tell us how much of the warming we have observed so far has happened naturally, and how much is driven by human emissions of greenhouse gases. Human activities are estimated to have increased the rate of warming by 200 times over natural levels and warmed the planet by around 1.2°C since the start of the Industrial Revolution. Current predictions are that the planet is still heading for up to 3.5°C of warming above pre-industrial levels by the end of this century.

When did scientists first learn about greenhouse gases? 

The world was introduced to the greenhouse effect in the 1850s –through the work of scientists like the Irish physicist John Tyndall and the American scientist Eunice Foote. They found that atmospheric gases such as carbon dioxide were trapping heat. The knowledge made it to New Zealand in 1912 when one of the first climate change reporters in NZ wrote for the Rodney and Otamatea Times stating that the warming effect from burning coal "may be considerable in a few centuries."

What does climate change mean for Aotearoa? How will our climate change in my lifetime?

We are already seeing the impacts of climate change in Aotearoa.  Temperatures are increasing significantly in many parts of the country and sea levels are rising - the average sea level has increased by nearly 30cm compared to 100 years ago. We are seeing the physical and environmental impacts of these changes. According to research from Statistics NZ and the Ministry for the Environment coastal erosion rates are increasing, coastal flood frequency is increasing, growing seasons are changing, and environments are becoming uninhabitable for some of our native species.

All these changes will have flow on effects to the economy, our primary industries and to people and communities. Changing temperatures and rainfall patterns will affect where and how well different crops can grow, while more extreme weather events increase the damage to houses, infrastructure and businesses.

Is it possible to tie extreme events to climate change, or are they just weather?  

We know that extreme weather, like floods, fires, heatwaves, and hurricanes are natural events. We also know that climate change is likely to lead to more of these extreme weather events. Scientists use weather records and climate models to work out how much human activities have increased the likelihood of extreme events.  
 
Much like doctors can study how smoking cigarettes affects cancer rates by comparing smokers and non-smokers, climate scientists can study extreme events by comparing our Earth with a hypothetical Earth, untouched by greenhouse gas emissions. This approach was used to study a storm in 2021 that caused flooding through Germany, Belgium, Luxembourg and the Netherlands and killed more than 200 people. The research found that climate change had made storms such as this nine times more likely to occur compared to a world without climate change. 

What do we need to do to stop climate change? 

Scientists have worked out what we need to do to stop the world getting warmer and warmer. The most important step is to stop emitting carbon dioxide, as this gas is the main driver of climate change.

If we are going to stop temperatures from rising more than 1.5°C above pre-industrial levels, carbon dioxide emissions need to peak within this decade and go to zero by the middle of the century. Emissions of the other main greenhouse gases like methane and nitrous oxide need to also reduce significantly from current levels, but do not need to reduce all the way to zero.

Can you remove greenhouse gases from the atmosphere?

Yes, it is possible either through natural or mechanical processes. At the moment growing trees – which store carbon from the atmosphere as they grow – is the main way of removing greenhouse gases from the atmosphere in New Zealand.  Other countries are heavily investing in carbon capture and storage where CO2 is captured after combustion of fossil fuels, compressed and injected underground for long term permanent storage.   There are other emerging technologies that can capture carbon dioxide from the air and pump it back underground. However, these processes are expensive and need further development. It is better to reduce greenhouse gas emissions in the first place.

To achieve long term net zero, it is important to focus on reducing and avoiding emissions wherever possible, so that we can balance out areas where it is very difficult to reduce them.

How do we measure how much carbon trees can remove from the atmosphere, and why is doing it important? 

Trees store carbon dioxide as they grow, reducing the amount of carbon dioxide in the atmosphere. However, this carbon dioxide is released if the tree burns down or is cut down.

Forests – where large areas of land are covered in trees – play an important role in removing emissions. It is important to know how much of New Zealand is covered in forest, but many factors such age, type of tree, where it is and how it is managed can make a difference to how much is stored.

Getting all this information is difficult and the Ministry for the Environment uses a variety of techniques like monitored plots, computer modelling, and satellite imagery. This produces an estimate that is updated and revised in the Greenhouse gas inventory as better information becomes available.