Carbon dioxide levels over Australia rose even after COVID-19 forced global emissions down. Here’s why

Zoe Loh, CSIRO; Helen Cleugh, CSIRO; Paul Krummel, CSIRO, and Ray Langenfelds, CSIRO

COVID-19 has curtailed the activities of millions of people across the world and with it, greenhouse gas emissions. As climate scientists at the Cape Grim Baseline Air Pollution Station, we are routinely asked: does this mean carbon dioxide concentrations in the atmosphere have fallen?

The answer, disappointingly, is no. Throughout the pandemic, atmospheric carbon dioxide (CO₂) levels continued to rise.

In fact, our measurements show more CO₂ accumulated in the atmosphere between January and July 2020 than during the same period in 2017 or 2018.

Emissions from last summer’s bushfires may have contributed to this. But there are several other reasons why COVID-19 has not brought CO₂ concentrations down at Cape Grim – let’s take a look at them.

Measuring the cleanest air in the world

Cape Grim is on the northwest tip of Tasmania. Scientists at the station, run by the CSIRO and Bureau of Meteorology, have monitored and studied the global atmosphere for the past 44 years.

The air we monitor is the cleanest in the world when it blows from the southwest, off the Southern Ocean. Measurements taken during these conditions are known as “baseline concentrations”, and represent the underlying level of carbon dioxide in the Southern Hemisphere’s atmosphere.

The Cape Grim station measures the cleanest air in the world.
Bureau of Meteorology

A drop in the CO₂ ocean

Emissions reductions due to COVID-19 started in China in January, and peaked globally in April. Our measurements show atmospheric CO₂ levels rose during that period. In January 2020, baseline CO₂ was 408.3 parts per million (ppm) at Cape Grim. By July that had risen to 410 ppm.

Since the station first began measurements in 1976, carbon dioxide levels in the atmosphere have increased by 25%, as shown in the graph below. The slowdown in the rate of carbon emissions during the pandemic is a mere tug against this overall upward trend.

The CO₂ increase is due to the burning of fossil fuels for energy, and land use change such as deforestation which leaves fewer trees to absorb CO₂ from the air, and changes the uptake and release of carbon in the soils.

Baseline CO₂ record from Cape Grim.
Author provided

Atmospheric transport

Large air circulation patterns in the atmosphere spread gases such as CO₂ around the world, but this process takes time.

Most emissions reduction due to COVID-19 occurred in the Northern Hemisphere, because that’s where most of the world’s population lives. Direct measurements of CO₂ in cities where strict lockdown measures were imposed show emissions reductions of up to 75%. This would have reduced atmospheric CO₂ concentrations locally.

But it will take many months for this change to manifest in the Southern Hemisphere atmosphere – and by the time it does, the effect will be significantly diluted.

Natural ups and downs

Emissions reductions during COVID-19 are a tiny component of a very large carbon cycle. This cycle is so dynamic that even when the emissions slowdown is reflected in atmospheric CO₂ levels, the reduction will be well within the cycle’s natural ebb and flow.

Here’s why. Global carbon emissions have grown by about 1% a year over the past decade. This has triggered growth in atmospheric CO₂ levels of between 2 and 3 ppm per year in that time, as shown in the graph below. In fact, since our measurements began, CO₂ has accumulated more rapidly in the atmosphere with every passing decade, as emissions have grown.

Annual growth in CO₂ at Cape Grim since 1976. Red horizontal bars show the average growth rate in ppm/year each decade.
Author provided

But although CO₂ emissions have grown consistently, the resulting rate of accumulation in the atmosphere varies considerably each year. This is because roughly half of human emissions are mopped up by ecosystems and the oceans, and these processes change from year to year.

For example, in southeast Australia, last summer’s extensive and prolonged bushfires emitted unusually large amounts of CO₂, as well as changing the capacity of ecosystems to absorb it. And during strong El Niño events, reduced rainfall in some regions limits the productivity of grasslands and forests, so they take up less CO₂.

The graph below visualises this variability. It shows the baseline CO₂ concentrations for each year, relative to January 1. Note how the baseline level changes through a natural seasonal cycle, how that change varies from year to year and how much CO₂ has been added to the atmosphere by the end of the year.

Daily baseline values for CO₂ for each year from 1977 relative to 1 January for that year — Daily baseline values for CO2 for each year from 1977 relative to 1 January for that year.
Author provided

The growth rate has been as much as 3 ppm per year. The black line represents 2020 and lines for the preceding five years are coloured. All show recent annual growth rates of about 2-3 ppm/year – a variability in the range of about 1 ppm/year.

Research in May estimated that due to the COVID-19 lockdowns, global annual average emissions for 2020 would be between 4.2% and 7.5% lower than for 2019.

Let’s simplistically assume CO₂ concentration growth reduces by the same amount. There would be 0.08-0.23 ppm less CO₂ in the atmosphere by the end of 2020 than if no pandemic occurred. This variation is well within the natural 1 ppm/year annual variability in CO₂ growth.

CO₂ is released in industrial emissions — CO₂ levels in the atmosphere are increasing due to fossil fuel burning and land use change.
Shutterstock

The road ahead

It’s clear COVID-19 has not solved the climate change problem. But this fact helps us understand the magnitude of change required if we’re to stabilise the global climate system.

The central aim of the Paris climate agreement is to limit global warming to well below 2℃, and pursue efforts to keep it below 1.5℃. To achieve this, global CO₂ emissions must decline by 3% and 7% each year, respectively, until 2030, according to the United Nations Emissions Gap Report.

Thanks to COVID-19, we may achieve this reduction in 2020. But to lock in year-on-year emissions reductions that will be reflected in the atmosphere, we must act now to make deep, significant and permanent changes to global energy and economic systems.

The lead author, Zoe Loh, discusses the CO₂ record from Cape Grim in Fight for Planet A, showing now on the ABC.

Zoe Loh, Senior Research Scientist, CSIRO; Helen Cleugh, Senior research scientist, CSIRO Climate Science Centre, CSIRO; Paul Krummel, Research Group Leader, CSIRO, and Ray Langenfelds, Scientist at CSIRO Atmospheric Research, CSIRO

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Climate explained: why higher carbon dioxide levels aren’t good news, even if some plants grow faster

Sebastian Leuzinger, Auckland University of Technology

Climate Explained is a collaboration between The Conversation, Stuff and the New Zealand Science Media Centre to answer your questions about climate change.

If you have a question you’d like an expert to answer, please send it to climate.change@stuff.co.nz

If carbon dioxide levels were to double, how much increase in plant growth would this cause? How much of the world’s deserts would disappear due to plants’ increased drought tolerance in a high carbon dioxide environment?

Compared to pre-industrial levels, the concentration of carbon dioxide (CO₂) in the atmosphere will have doubled in about 20 to 30 years, depending on how much CO₂ we emit over the coming years. More CO₂ generally leads to higher rates of photosynthesis and less water consumption in plants.

At first sight, it seems more CO₂ can only be beneficial to plants, but things are a lot more complex than that.

Let’s look at the first part of the question.

Some plants do grow faster under elevated levels of atmospheric CO₂, but this happens mostly in crops and young trees, and generally not in mature forests.

Even if plants grew twice as fast under doubled CO₂ levels, it would not mean they strip twice as much CO₂ from the atmosphere. Plants take carbon from the atmosphere as they grow, but that carbon is going straight back via natural decomposition when plants die or when they are harvested and consumed.

At best, you might be mowing your lawn twice as often or harvesting your plantation forests earlier.

The most important aspect is how long the carbon stays locked away from the atmosphere – and this is where we have to make a clear distinction between increased carbon flux (faster growth) or an increasing carbon pool (actual carbon sequestration). Your bank account is a useful analogy to illustrate this difference: fluxes are transfers, pools are balances.

The global carbon budget

Of the almost 10 billion tonnes (gigatonnes, or Gt) of carbon we emit every year through the burning of fossil fuels, only about half accumulates in the atmosphere. Around a quarter ends up in the ocean (about 2.4 Gt), and the remainder (about 3 Gt) is thought to be taken up by terrestrial plants.

While the ocean and the atmospheric sinks are relatively easy to quantify, the terrestrial sink isn’t. In fact, the 3 Gt can be thought of more as an unaccounted residual. Ultimately, the emitted carbon needs to go somewhere, and if it isn’t the ocean or the atmosphere, it must be the land.

So yes, the terrestrial system takes up a substantial proportion of the carbon we emit, but the attribution of this sink to elevated levels of CO₂ is difficult. This is because many other factors may contribute to the land carbon sink: rising temperature, increased use of fertilisers and atmospheric nitrogen deposition, changed land management (including land abandonment), and changes in species composition.

Current estimates assign about a quarter of this land sink to elevated levels of CO₂, but estimates are very uncertain.

In summary, rising CO₂ leads to faster plant growth – sometimes. And this increased growth only partly contributes to sequestering carbon from the atmosphere. The important questions are how long this carbon is locked away from the atmosphere, and how much longer the currently observed land sink will continue.

The second part of the question refers to a side-effect of rising levels of CO₂ in the air: the fact that it enables plants to save water.

Plants regulate the exchange of carbon dioxide and water vapour by opening or closing small pores, called stomata, on the surface of their leaves. Under higher concentrations of CO₂, they can reduce the opening of these pores, and that in turn means they lose less water.

This alleviates drought stress in already dry areas. But again, the issue is more complex because CO₂ is not the only parameter that changes. Dry areas also get warmer, which means that more water evaporates and this often compensates for the water-saving effect.

Overall, rising CO₂ has contributed to some degree to the greening of Earth, but it is likely that this trend will not continue under the much more complex combination of global change drivers, particularly in arid regions.

Sebastian Leuzinger, Professor, Auckland University of Technology

This article is republished from The Conversation under a Creative Commons license. Read the original article.

World greenhouse gas levels made unprecedented leap in 2016

File 20171031 18689 lpras9.jpg?ixlib=rb 1.1 — Human activity, along with a strong El Nino, drove 2016 greenhouse gas levels to new heights.
AAP Image/Dave Hunt

Paul Fraser, CSIRO; Paul Krummel, CSIRO, and Zoe Loh, CSIRO

Global average carbon dioxide concentrations rose by 0.8% during 2016, the largest annual increase ever observed. According to figures released overnight by the World Meteorological Organisation, atmospheric CO₂ concentrations reached 403.3 parts per million. This is the highest level for at least 3 million years, having climbed by 3.3 ppm relative to the 2015 average.

The unprecedented rise is due to carbon dioxide emissions from fossil fuels (coal, oil and gas) and the strong 2015-16 El Niño event, which reduced the capacity of forests, grasslands and oceans to absorb carbon dioxide from the atmosphere.

Greenhouse gas levels are unprecedented in modern times.
WMO

The figures appear in the WMO’s annual Greenhouse Gas Bulletin. This is the authoritative source for tracking trends in greenhouse gases that, together with temperature-induced increases in atmospheric water vapour, are the major drivers of current climate change.

Laboratories around the world, including at CSIRO and the Bureau of Meteorology in Australia, measure atmospheric greenhouse gas concentrations at more than 120 locations. The gases include carbon dioxide, methane and nitrous oxide, as well as synthetic gases such as chlorofluorocarbons (CFCs).

At Cape Grim in Tasmania, we observed a corresponding increase during 2016 of 3.2 ppm, also the highest ever observed.

For 2017 so far, Cape Grim has recorded a smaller increase of 1.9 ppm. This possibly reflects a reduced impact of El Niño on atmospheric carbon dioxide growth rates this year.

Long-term record of background carbon dioxide from Cape Grim, located at the northwest tip of Tasmania.
CSIRO/BoM

For roughly 800,000 years before industrialisation began (in around the year 1750), carbon dioxide levels remained below 280 parts per million, as measured by air trapped in Antarctic ice. Geological records suggest that the last time atmospheric levels of carbon dioxide were similar to current levels was 3-5 million years ago. At that time, the climate was 2-3℃ warmer than today’s average, and sea levels were 10 to 20 metres higher than current levels.

Human-driven change

The extraordinarily rapid accumulation of CO₂ in the atmosphere over the past 150 years is overwhelmingly and unequivocally due to human activity.

Methane is the second-most-important long-lived greenhouse gas in the atmosphere, with 40% coming from natural sources such as wetlands and termites and the remaining 60% from human activities including agriculture, fossil fuel use, landfills and biomass burning.

In 2016, global atmospheric methane also hit record levels, reaching 1,853 parts per billion, an increase of 9 ppb or 0.5% above 2015 levels. At Cape Grim, methane levels climbed by 6 ppb in 2016, or 0.3% above 2015 levels.

Nitrous oxide is the third-most-important greenhouse gas, of which [around 60% comes from natural sources such as oceans and soils], and 40% from fertilisers, industrial processes and biomass burning.

In 2016, global atmospheric nitrous oxide hit a record 328.9 ppb, having climbed by 0.8 ppb (0.2%) above 2015 levels. At Cape Grim, we observed the same annual increase of 0.8 ppb.

If we represent the climate change impact of all greenhouse gases in terms of the equivalent amount of CO₂, then this “CO₂-e” concentration in the atmosphere in 2016 would be 489 ppm. This is fast approaching the symbolic milestone of 500 ppm.

These record greenhouse gas levels are consistent with the observed rise in global average temperatures, which also hit record levels in 2016.

The only way to reduce the impact is to significantly reduce our greenhouse gas emissions. The Kyoto Protocol and the subsequent Paris Agreement are important first steps in a long and challenging process to reduce such emissions. Their immediate success and ultimate strengthening will be crucial in keeping our future climate in check.

The authors thank Dr David Etheridge for his advice on the use of proxy measurements to infer carbon dioxide levels in past atmospheres.

Paul Fraser, Honorary Fellow, CSIRO; Paul Krummel, Research Group Leader, CSIRO, and Zoe Loh, Research Scientist, CSIRO

This article was originally published on The Conversation. Read the original article.

Current emissions could already warm world to dangerous levels: study

Andrew Glikson, Australian National University

Current greenhouse gas concentrations could warm the world 3-7℃ (and on average 5℃) over coming millennia. That’s the finding of a paper published in Nature today.

The research, by Carolyn Snyder, reconstructed temperatures over the past 2 million years. By investigating the link between carbon dioxide and temperature in the past, Snyder made new projections for the future.

The Paris climate agreement seeks to limit warming to a “safe” level of well below 2℃ and aim for 1.5℃ by 2100. The new research shows that even if we stop emissions now, we’ll likely surpass this threshold in the long term, with major consequences for the planet.

What is climate sensitivity?

How much the planet will warm depends on how temperature responds to greenhouse gas concentrations. This is known as “climate sensitivity”, which is defined as the warming that would eventually result (over centuries to thousands of years) from a doubling of CO₂ concentrations in the atmosphere.

The measure of climate sensitivity used by the Intergovernmental Panel on Climate Change (IPCC) estimates that a doubling of CO₂ will lead to 1.5-4.5℃ warming. A doubling of CO₂ levels from before the Industrial Revolution (280 parts per million) to 560ppm would likely surpass the stability threshold for the Antarctic ice sheet.

As the world warms, it triggers changes in other systems, which in turn cause the world to warm further. These are known as “amplifying feedbacks”. Some are fast, such as changes in water vapour, clouds, aerosols and sea ice.

Others are slower. Melting of the large ice sheets, changes in the distribution of forests, plants and ecosystems, and methane release from soils, tundra or ocean sediments may begin to come into play on time scales of centuries or less.

Other research has shown that during the mid-Pliocene epoch (about 4.5 million years ago) atmospheric CO₂ levels of about 365-415ppm were associated with temperatures about 3–4 °C warmer than before the Industrial Revolution. This suggests that the climate is more sensitive than we thought.

This is concerning because since the 18th century CO₂ levels have risen from around 280ppm to 402ppm in April this year. The levels are currently rising at around 3ppm each year, a rate unprecedented in 55 million years. This could lead to extreme warming over the coming millennia.

Temperature histories from paleoclimate data (green line) compared to the history based on modern instruments (blue line) suggest that global temperature is warmer now than it has been in the past 1,000 years, and possibly longer.
NASA, Author provided

More sensitive than we thought

The new paper recalculates this sensitivity again – and unfortunately the results aren’t in our favour. The study suggests that stabilisation of today’s CO₂ levels would still result in 3-7℃ warming, whereas doubling of CO₂ will lead to 7-13℃ warming over millennia.

The research uses proxy measurements for temperature (such as oxygen isotopes and magnesium-calcium ratios from plankton) and for CO₂ levels, calculated for every 1,000 years back to 2 million years ago.

Some other major findings include:

The Earth cooled gradually to about 1.2 million years ago, followed by an increase in the size of ice sheets around 0.9 million years ago, and then followed by around 100,000-year-long glacial cycles.

Over the last 800,000 years, and particularly during glacial cycles, atmospheric greenhouse gas concentrations and global temperature were closely linked.

The study shows that for every 1℃ of global average warming, Antarctica warms by 1.6℃.

So what does all this mean for the future?

Global warming past and future, triggered initially by either changes in solar radiation or by greenhouse gas emissions, is driven mainly by amplifying feedbacks such as warming oceans, melting ice, drying vegetation in parts of the continents, fires and methane release.

Current CO₂ levels of around 400ppm, combined with methane (rising toward 1,900 parts per billion) and nitric oxide (around 310ppb), are already driving such feedbacks.

According to the new paper, such greenhouse gas levels are committing the Earth to extreme rises of temperature over thousands of years, with consequences consistent with the large mass extinctions.

The IPCC suggests warming will increase steadily as greenhouse gases increase. But the past shows there will likely be abrupt shifts, local reversals and tipping points.

Abrupt freezing events, known as “stadials”, follow peak temperatures in the historical record. These are thought to be related to the Mid-Atlantic Ocean Current. We’re already seeing marked cooling of ocean regions south of Greenland, which may herald collapse of the North Atlantic Current.

A global temperature map for 2015 showing the cold water region in the North Atlantic Ocean.
NASA, Author provided

As yet we don’t know the details of how different parts of the Earth will respond to increasing greenhouse gases through both long-term warming and short-term regional or local reversals (stadials).

Unless humanity develops methods for drawing down atmospheric CO₂ on a scale required to cool the Earth to below 1.5°C above pre-industrial temperature, at the current rate of CO₂ increase of 3ppm per year we are entering dangerous uncharted climate territory.

Andrew Glikson, Earth and paleo-climate scientist, Australian National University

This article was originally published on The Conversation. Read the original article.