What is going on with climate change

Ice Ages happen when CO2 levels in the atmosphere are around 180 parts per million. The cyclical warmer periods in between Ice Ages – known as interglacial periods – happen at around 280 parts per million. This has been the case for all Ice Age cycles over the past 800,000 years; as far back as scientists have measurements from ice cores, in fact. Today, however, emissions from human activities have caused atmospheric CO2 levels to reach around 410 parts per million; far above the level for being a natural warm period within these 800,000 years, and it is still rising.

Ice Ages are triggered and paced by changes to incoming solar radiation, as variations in the Earth’s orbit change the way the Sun’s energy is distributed. In the Northern Hemisphere, the difference between summer and winter insolation – the amount of sunlight that reaches Earth – varies over cycles of 100,000, 40,000 and 21,000 years. When summer solar radiation is reduced, summer warming is unable to melt the snow that has built up over the previous winter. This kick-starts the process that leads to an Ice Age – which last happened on Earth about 20,000 years ago.

These natural variations in solar radiation are subtle, and scientists know they are too weak to build an Ice Age by themselves. However, their effect is amplified by feedback loops that make them stronger. For example, when the Earth’s surface turns white due to increased snow and ice cover, it becomes more reflective and so cools the planet further. Variation in CO2 levels is also an important feedback loop in creating an Ice Age. Part of this feedback loop relates to changes in how much CO2 the ocean stores.

As the polar oceans cool, they become more productive. This is because cooler surface water is less buoyant than warm water, and so encourages nutrient-rich subsurface water to ‘upwell’ into the surface layer of water – the ‘sunlit zone’. Nutrient-rich water absorbs more atmospheric CO2 into the shells and bones of marine creatures and plants. This reduces the amount of CO2 in the atmosphere and amplifies the cooling of the Earth further. As the Earth’s orbit around the Sun shifts and the summers become warmer, the ice begins to melt and the opposite process occurs, leading to global warming.

The pace of today’s rise of CO2 levels in the atmosphere is much faster than for any glacial cycle. In the last 60 years alone, emissions from human activities using fossil fuels have caused CO2 levels to increase by about 100 parts per million, taking us to 410 parts per million in total. It took 10,000 years for CO2 levels to increase by 100 parts per million naturally, following the last Ice Age.

The amount of CO2 in the atmosphere is also higher than at any other point in human history. The last time the world had a CO2 concentration of 410 parts per million was between 5.0–3.5 million years ago, when the world was 3–4 degrees warmer than today. Greenland and West Antarctica were free of ice and sea levels were 15–20 metres higher than today.

Latest IPCC climate report warns that rising greenhouse-gas emissions could soon outstrip the ability of many communities to adapt.

• Jeff Tollefson

1. Jeff Tollefson

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The climate crisis has already negatively affected places such as Bangladesh, where river-bank erosion has cost people their homes.Credit: Zakir Hossain Chowdhury/Barcroft Media/Getty

The negative impacts of climate change are mounting much faster than scientists predicted less than a decade ago, according to the latest report from a United Nations climate panel. Many impacts are unavoidable and will hit the world’s most vulnerable populations hardest, it warns — but collective action from governments to both curb greenhouse-gas emissions and prepare communities to live with global warming could yet avert the worst outcomes.

“The cumulative scientific evidence is unequivocal,” says Maarten van Aalst, a climate scientist who heads the Red Cross Red Crescent Climate Centre in Enschede, the Netherlands, and is a co-author of the report. “Any further delay in global action on adaptation and mitigation will miss a brief and rapidly closing window of opportunity to secure a liveable and sustainable future for all.”

IPCC climate report: Earth is warmer than it’s been in 125,000 years

The report, released on 28 February, is the second instalment of the latest climate assessment from the UN Intergovernmental Panel on Climate Change (IPCC). Issued last August, the first instalment focused on recent climate science, whereas the latest one looks at the impacts of climate change on people and ecosystems. It will be followed in early April by a third instalment that evaluates humanity’s options for battling climate change, including ways of reducing greenhouse-gas emissions. This is the sixth such assessment from the IPCC in a little over three decades, and the warnings have only become more dire. Advocates hope the latest assessment will finally spur governments to tackle the climate crisis decisively.

“I’ve seen many scientific reports in my time, but nothing like this,” said UN secretary-general António Guterres during a press conference unveiling the report. It is a “damning indictment of failed climate leadership”, he added.

Key points from the report:

• Between 3.3 billion and 3.6 billion people — more than 40% of the world’s population — live in places and in situations that are “highly vulnerable to climate change”, the report estimates. Some are already experiencing the effects of climate change, which vary by region and are driven by factors such as geography, how that region is governed and its socio-economic status. The report also references for the first time “historical and ongoing patterns of inequity such as colonialism” that contribute to many regions’ vulnerability to climate change.

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• Although additional finance and planning could help many communities to improve their preparations for climate change, humanity will soon hit “hard limits” to its ability to adapt if temperatures continue to rise, the report says. For instance, coastal communities can temporarily buffer themselves from extreme storms by restoring coral reefs, mangroves and wetlands, but rising seas will eventually overwhelm such efforts, resulting in coastal erosion, flooding and loss of freshwater resources.

• Climate change has already caused death and suffering across the world, and it will continue to do so. In addition to contributing to deaths by helping to trigger disasters such as fires and heatwaves, it has affected public health in various ways. Smoke inhalation from fires has contributed to cardiovascular and respiratory problems, for instance, and increased rainfall and flooding has led to the spread of diseases such as cholera. Mental-health issues, tied to the trauma of living through extreme events and to loss of livelihood and culture, are also on the rise.

• If global temperatures rise by more than 1.5 °C above pre-industrial levels, some environmental changes could become irreversible, depending on the magnitude and duration of the ‘overshoot’ beyond this threshold. In forests and Arctic permafrost zones that act as carbon dioxide reservoirs, for instance, extreme global warming could lead to the release of excess carbon emissions, which would in turn drive further warming — a self-perpetuating cycle.

• Sustainable economic development must include protection for biodiversity and natural ecosystems, which secure resources such as fresh water and coastlines that shield against the effects of storms, the report says. Multiple lines of evidence suggest that maintaining the resilience of biodiversity and ecosystems as the climate warms will depend on “effective and equitable conservation of approximately 30% to 50% of Earth’s land, freshwater and ocean areas”.

More than 270 researchers from 67 countries authored the latest IPCC report. Here’s what some are saying about its importance:

Adelle Thomas, a geographer at the University of the Bahamas in Nassau. The most important message coming from the report from my perspective is that losses and damages are widespread and being felt now. Unfortunately, these negative impacts of climate change are disproportionately affecting the most vulnerable and marginalized communities around the world. Also crucial is evidence showing that people and ecosystems are already reaching limits to adaptation, where they have surpassed their capacities to prevent negative impacts of climate change.

As a scientist from the Bahamas, one of the low-lying coastal countries that are at high risk from climate change, I hope that this report provides an impetus for policymakers to limit warming to 1.5 °C, urgently ramp up adaptation and address loss and damage.

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Edwin Castellanos, director of the Sustainable Economic Observatory at the University of the Valley of Guatemala in Guatemala City. This report combines two messages, one of urgency and one of hope: urgency to act, not only to drastically reduce emissions in the near term, but to increase our actions to adapt to the impacts already observed and to come. And there is hope from knowing that we are still in time to take these actions.

My hope is that this report will highlight the need for developed countries to support developing countries, particularly with financial resources to reduce the vulnerability of people, particularly those at higher risk: the poor, the marginalized and Indigenous peoples.

Sarah Cooley, director of climate science at the Ocean Conservancy, a conservation group based in Washington DC. This report assesses how local communities are rising to the challenge of climate change and have become leaders on climate adaptation and climate planning. It evaluates the climate adaptations that communities have already tried, and it identifies the features of successful, equitable activities, as well as opportunities for even bigger changes.

It also confirms that any more delay in climate action is going to close off opportunities to head off the worst impacts of climate. But the good news is, there are more details than ever about how the global community can meet the challenge effectively, despite our slow start.

Ibidun Adelekan, a geographer at the University of Ibadan in Nigeria. The report underscores the fact that the capacity of individuals and local communities to cope and adapt to the risks from climate change is very limited without adaptation-planning efforts supported by governments. There is need for collaboration among citizens, scientists, the private sector and policymakers to develop feasible adaptation plans, through the integration of different knowledge systems — including local and Indigenous knowledge.

Rawshan Ara Begum, an economist from Bangladesh who studies sustainable development at Macquarie University in Sydney, Australia. This report provides a range of climate-adaptation options for reducing vulnerability and enhancing resilience. As a citizen of a vulnerable country, I have hopes that global leaders will take urgent, accelerated action to adapt to climate change, while making rapid, deep cuts in greenhouse-gas emissions.

Bangladesh is one of the most vulnerable countries in the world, owing to climate change and sea-level rise. This will further worsen the country’s current challenges, including extreme poverty, income inequality, economic and non-economic losses and damages, and low adaptive capacity. Urgent and accelerated action is required.

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