What is the problem with climate change?

It is causing more frequent and worse heat waves, wildfires, floods, and storms. These impact human health, farming, fisheries, forestry, food security, infrastructure, drinking water supplies, and biodiversity. They cause social stress and have economic costs (including disaster relief, firefighting, lost crops, lost tourism, increased or no insurance cover).

Infrastructure costs include damage and failure of electrical and communication services, sewage treatment, landfills, stormwater drains, roads, buildings, harbours, airports, railway lines.

Biodiversity costs include loss of marine and terrestrial plant production, altered ecology perhaps favouring pest species and pathogens (viruses, bacteria, fungi, parasites), and further declines of threatened species.

These impacts get increasingly severe with more global warming and will affect everyone now and future generations.

Short video explainers from the BBC What is climate change? and Climate Check. and The New York Times.

What is the trend with greenhouse gases?

Their concentration in the atmosphere is at its highest for at least two million years. Half the releases from fossil fuel burning are captured in the oceans and on land, leaving half in the atmosphere.

That fossil fuel emissions of greenhouse gas cause global warming has been known since the late 1980s.

Can we prevent climate change from getting worse?

Yes, by reducing its causes, namely the burning of fossil fuels. In addition, increasing carbon storage by vegetation on land and in the sea (e.g., forests, corals, shellfish, plankton that sink to the seabed) will reduce atmospheric carbon dioxide over time.

The longer society delays in addressing climate change the greater the costs to do so will be. Some economic assessments estimate that the cost of addressing greenhouse gas emissions is half the cost of doing nothing. The cost of keeping global warming to 2 ^oC is double the cost of keeping it to 1.5 ^oC.

Can we not use technology to adapt to climate change?

Yes, technology will help, especially by replacing fossil fuel as an energy source with non-carbon emitting sources (e.g. solar, wind, wave and hydro-power). However, technological (e.g., air-conditioning) and infrastructure (e.g., sea walls) adaptations will become more expensive and not protect natural ecosystems or reduce natural disasters (fires, storms). Also, much of the hypothesised technologies do not exist or would be more expensive than converting society to non-fossil fuels earlier.

According to several eminent climate scientists, there is no proven way of achieving “net-zero”  carbon dioxide to date. Thus, action is needed now to limit emissions because the amount of greenhouse gases needing to be addressed increases every day.

How much has the world warmed so far?

By just over 1^oC globally since the late 19th century. Warming varies a lot geographically, being greater in the high latitudes of the northern hemisphere and much less in the Southern Ocean. However, New Zealand air temperatures have also warmed by 1^oC from 1909 to 2018.

There has been greater warming over land (1.4^oC) than the sea (0.8^oC), but because the ocean occupies 71% of the planet it has a dominant influence on the global annual average temperature reported. This difference is because the ocean absorbs heat more slowly, and loses more heat through evaporation which is transported higher into the atmosphere through higher humidity above the ocean, more than land (Byne 2020). Thus, drier lands warm more.

How much has sea level risen?

Globally, by 19 cm from 1901 to 2010, an average of 1.7 mm per year. The amount varies geographically due to land level changes and ocean height variation. In New Zealand, sea-level has risen faster, i.e., by an average of 2.4 mm per year from 1961 to 2018 (before 1960 it rose at 1.2 mm/year). In itself this seems insignificant but combined with high tides or storms, it means greater coastal flooding, landscape change and saltwater intrusion into wetlands. In New Zealand, the sea level will rise a further 0.2 to 0.9 m (above a 2005 baseline) by 2050 and 2100 respectively.

Is there any good side to global warming?

While there may be, on average, milder winters and less snow, the negatives greatly outweigh the positives. In some locations, this may lengthen the growing season in high latitudes, leading to early harvests, and increase decomposition rates. Russia may gain farmable land from the thawing of permafrost. This win/lose index shows how countries ability to adapt depends on both the degree of climate change and their preparedness.

Given good data on trends and understanding of ecosystems, it may be possible for farming and fisheries to adapt to climate change in some high latitudes, but not in low latitudes where it will be too hot. However, changes in atmospheric circulation may be resulting in more extreme cold weather in some regions such as northern America and Europe. These extreme events will have negative effects on farming as well as human health.

Although higher carbon dioxide levels can increase plant growth rates this requires more moisture on land and additional nutrients in the sea which are generally not available. Thus a carbon dioxide “fertilisation” effect is unlikely. Ocean phytoplankton productivity is predicted to decline due to climate change.

Why does global warming affect the weather?

Increased temperature results in more energy in the climate system. This manifests in stronger winds, greater evaporation of moisture from land and ocean leading to more clouds and extreme rainfall events, drier land and vegetation, longer droughts and more floods. One analysis indicates that weather conditions that promote wildfire in Australia are at least two times greater due to human-induced climate change; another that human-caused climate change has led to a 20 times increase in Marine Heat Waves.

What role has the ocean in climate change?

By absorbing about 90% of the energy from global warming the ocean greatly slows the rate of climate change. While the ocean has warmed by 1 ^oC since 1900, and the sea level has risen 25 cm since 1880, there is considerable geographic variation in warming and sea-level rise.

Is there any scientific debate about whether global warming (climate change) is happening? 

No. The climate data show it has been happening for decades. A few people (but not climate scientists) deny the role of our burning of fossil fuels as contributing to carbon dioxide and other greenhouse gases in the atmosphere (which is the cause of global warming and predicted decades ago). However, there is no other reasonable explanation for global warming, and carbon dioxide concentrations only make sense when fossil fuel burning is accounted for.

Good science distinguishes between the facts (data) and theories, the known and unknown, but also provides a reasoned argument (theory) as to cause and effect. As research progresses, some facts and theories become more certain and others are discarded. Each IPCC assessment has reassessed the facts and become more certain and the causes and projected effects of climate change.

How come the media portrayed uncertainty in whether fossil fuel emissions caused climate change?

There were organised fossil fuel industry supported campaigns to promote uncertainty so as to delay any action to reduce fossil fuel use. This strategy has been called the “tobacco playbook” following the success of the tobacco industry using naive, mistaken, poorly informed and compromised scientists to debate whether smoking was harmful. This debate suits the media need for controversy and provides a convenient excuse for people who do not want to change or have new regulations that affect their lifestyle. A nice rebuttal of the arguments against anthropogenic climate change is available on Skeptical Science. Their tactics may now be shifting from denial to deflection and delay tactics.

Are there win-win-win solutions for biodiversity restoration and climate change adaptation and mitigation? 

Yes, protected areas restore and conserve biodiversity which in turn captures and stores more carbon on land and sea.

Examples of “ecosystem-based management and adaptation“ are natural defences to reduce coastal erosion (e.g., mangroves, coral reefs), trees and parks that aid cooling in urban areas through shade and evapotranspiration, trees and vegetation that soak up water which is slowly released and reduces floods and droughts. Examples here for Australia.

How is progress in mitigating (reducing) the effects of climate change?

Not good at all. The black line on these graphs shows that trends in emissions are following the model (scenario) with the highest warming.

Further reading

For the world: IPCC, 2014: Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, R.K. Pachauri and L.A. Meyer (eds.)]. IPCC, Geneva, Switzerland, 151 pp. Also available at https://www.ipcc.ch/report/ar5/syr/

For New Zealand: Ministry for the Environment. 2020. National Climate Change Risk Assessment for Aotearoa New Zealand: Main report – Arotakenga Tūraru mō te Huringa Āhuarangi o Āotearoa: Pūrongo whakatōpū. Wellington: Ministry for the Environment. Some interesting expert comments on the report.

A nice overview regarding New Zealand “Our atmosphere and climate 2020 summary“.

For Australia State of the Climate 2020 report with comments on the global situation. For 2021 it is a dramatic reading: “2019-20 was an exceptionally intense period for climate-fuelled extreme weather…. An extraordinary run of events, including unprecedented fire seasons in Australia and the US, a record-breaking North Atlantic hurricane season, and an astonishing series of heat records, paint a sobering portrait of our escalating climate crisis. The latest science projects that by 2100, annual deaths from extreme heat worldwide will outstrip all COVID-19 deaths recorded in 2020. The cost of extreme weather disasters in Australia has more than doubled since the 1970s, reaching $35 billion for the decade 2010-2019. Australians are five times more likely to be displaced by a climate-fuelled disaster than someone living in Europe. In the Pacific, that risk is 100 times higher.

Maps and data on climate change for Australia and globally.

Covid drove a record drop in fossil fuel emissions from transport in 2020, showing where transport emissions will improve air quality and reduce climate change.

For Ireland, more extreme weather events are driven by climate change and getting increasingly worse: Ireland’s climate: A year of extremes, from wettest February to driest spring (via @IrishTimes)

A horrifying vision for Australia at 3 oC by 2100 based on current (insufficient) plans to curb greenhouse gas emissions: The risks to Australia of a 3°C warmer world.

Byrne M. 2020. Why does land warm up faster than the oceans? Carbon Brief.