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). Extreme events such as heatwaves and wildfire smoke kill people (hundreds during late 2019 Australian wildfire, and thousands hospitalised). Air pollution from fossil fuels in cities also affects human health and mortality rates.

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

A collection of photographs of 2021 heatwaves, wildfires, floods, landslides, cyclones and tornados around the world is here.

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.The New York Times, and IPCC 6th Assessment Report 2021 with an independent “explainer“.

How can we know that once off extreme weather events are caused by anthropogenic climate change?

At first, it was not possible to know if extreme weather events, including heatwaves, droughts and floods were due to climate change. But looking back it seems these indicators began in the 1960s. Now, the increasing frequency and severity of extreme weather events that break new long-time records leave no doubt as to the cause. They are affecting both developed and developing countries. Warmer air absorbs more moisture and this falls as rain. Warmer oceans and land increase air thermals leading to stronger winds. Changing atmospheric circulation patterns change rainfall patterns in space and time. As time goes on and data accumulates it has become easier to attribute an extreme weather event to anthropogenic climate, as does the World Weather Attribution website.

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 gases cause global warming has been known since the late 1980s.

Greenhouse gas emissions have been rising since the late 19th century and their effects on the climate became increasingly apparent since the 1980s, but signs of it were there since the 1960s.

The Climate Clock calculates the time that the annual average temperature will take to reach 1.5 oC. IT accounts for recent emissions, and because these are continuing to increase, this time gets earlier than stated in IPCC reports.

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.

The later reductions in greenhouse gas emissions are delayed the longer will be the withdrawal time it takes for atmospheric concentrations to decline. Even if emissions stopped now, it will take centuries to return to 1980s concentrations.

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?

Global mean surface temperature (over land and sea) has risen by just over 1^oC globally relative to the average from 1850 to 1900. Warming varies a lot geographically, being greater in the high latitudes of the northern hemisphere (Arctic region) and much less in the Southern Ocean. Most extreme temperatures are occurring in the low latitudes near the equator. 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 the 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.

The combination of melting sea ice and glaciers, and ocean expansion as it warms has set in motion sea-level rise of mm per decade that will continue for centuries.

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.

Measurements show that wind speed has increased in line with climate change, leading to increases in ocean current speeds (circulation) detectable down to 2000 m depth.

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. The ocean has also absorbed about 23% of the carbon dioxide emitted by human activities.

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.

Warming reduces the concentration of oxygen in the ocean, reducing oxic habitat for most marine species. Contrary to popular statements, the ocean is not a net contributor to the oxygen we breathe as explained in this article.

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.

Understanding of the physics underlying how the sun warmed the Earth developed over 200 years ago (1820s). How carbon dioxide and other gases may cause a greenhouse effect was understood in the late 19th century.  An appreciation of the significance of these greenhouse gases and the link to fossil fuel emissions emerged since the 1950s.

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 and in a book detailing how a mix of industry lobbyists and others tried to deny the facts. Their tactics may now be shifting from denial to deflection and delay tactics, and/or rhetoric with no significant investment in real change.

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. Soils, peatlands, and marine and freshwater sediments can be carbon sinks, sometimes called reservoirs and stores, because disturbance of these reservoirs may release greenhouse gases. Carbon dioxide and other greenhouse gases are also “stored” in water, with the ocean being the largest store by virtue of its size. Plants and other living matter also store carbon on a temporary basis.

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.

The global annual temperature has warmed by 0.3, 0.5, 0.7, 1.0 and almost 1.2 oC by 1980, 1990, 2000, 2010 and 2021 respectively, since pre-industrial times (1850-1900). About 0.2 oC per decade. Without zero carbon emissions from fossil fuels plus carbon removal from the atmosphere (for which no technology is currently operational at sufficient scale), the planet will warm to 1.5 oC by the early 2030s. as explained here.

What are the trends in emissions, impacts, and actions to reduce climate change?

The OECD Dashboard tracks these globally and nationally. The use of coal and oil is decreasing while renewable energy sources and natural gas is increasing. Energy use accounts for 80% of greenhouse gas emissions, industry 7% and agriculture almost 10%, and these vary by country.

The OECD Climate Action Monitor tracks the pledges by countries. In 2021 only 20% have made a zero-carbon pledge in law, another 20% proposed to and the remainder are considering it. These pledges only go a little more than halfway to meeting the targets necessary to curtail climate change. Lots of other interesting statistics here too.

What else is happening?

Increased carbon dioxide dissolved in the ocean as carbon acid is decreasing (acidifying) ocean pH. The ecological significance of this is a concern although unclear.

Unbelievably, governments continue to subsidise the use of the fossil fuels that are causing climate change.

What is the trend in evidence?

The evidence reviewed in each IPCC Assessment has confirmed the findings of its previous reports. The accumulation of field data improves predictions of future impacts of climate change. So now we know that the planet surface has warmed by an annual average of 1.2 oC since preindustrial times and is heading for 1.5 oC by the early 2030s (WMO 2021). Thus, extreme events such as heatwaves, floods, droughts, and wildfires, will increase in frequency and severity. Concurrently, the chronic effects of warming, glacier melting, ocean acidification and sea-level rise will accelerate. Hence the unprecedented global nature of the climate crisis is, directly and indirectly, affecting public health, business sector, property, infrastructure, food security and biodiversity. Adaptation by society may reduce such impacts, but only mitigation through reduced greenhouse gas emissions can reduce the occurrence of extreme events.

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/

United Nations Climate Action 2021. Key Findings.

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.

The Australian Climate Council produces information, news and advocates for addressing human-caused climate change.

World Meteorological Organisation 2021. State of the Global Climate 2020 (WMO-No. 1264).

Global emissions to hit 36.8 billion tonnes, beating last year’s record high

New research: nitrous oxide emissions 300 times more powerful than CO₂ are jeopardising Earth’s future

Eighteen countries showing the way to carbon zero [their emissions are declining]

Get a better understanding of the science of climate change in just 6 charts