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Carbon dioxide is a fertiliser for plants, so if its concentration increases in the atmosphere then plants will grow better. So what is the problem? – a question from Doug in Lower Hutt
Rising atmospheric carbon dioxide (CO₂) is warming our climate, but it also affects plants directly.
A tree planted in the 1850s will have seen its diet (in terms of atmospheric carbon dioxide) double from its early days to the middle of our century. More CO₂ generally leads to higher rates of photosynthesis and less water consumption in plants. So, at first sight, it seems that CO₂ can only be beneficial for our plants.
But things are a lot more complex than that. Higher levels of photosynthesis don’t necessarily lead to more biomass production, let alone to more carbon dioxide sequestration. At night, plants release CO₂ just like animals or humans, and if those respiration rates increase simultaneously, the turnover of carbon increases, but the carbon stock doesn’t. You can think of this like a bank account – if you earn more but also spend more, you’re not becoming any richer.
Even if plants grow more and faster, some studies show there is a risk for them to have shorter lifespans. This again can have negative effects on the carbon locked away in biomass and soils. In fact, fast-growing trees (e.g. plantation forests) store a lot less carbon per surface area than old, undisturbed forests that show very little growth. Another example shows that plants in the deep shade may profit from higher levels of CO₂, leading to more vigorous growth of vines, faster turnover, and, again, less carbon stored per surface area.
The effect of CO₂ on the amount of water plants use may be more important than the primary effect on photosynthesis. Plants tend to close their leaf pores slightly under elevated levels of CO₂, leading to water savings. In certain (dry) areas, this may indeed lead to more plant growth.
But again, things are much more complex and we don’t always see positive responses. Research we published in Nature Plants this year on grasslands around the globe showed that while dry sites can profit from more CO₂, there are complex interactions with rainfall. Depending on when the rain falls, some sites show zero or even negative effects in terms of biomass production.
Currently, a net amount of three gigatons of carbon are thought to be removed from the atmosphere by plants every year. This stands against over 11 gigatons of human-induced release of CO₂. It is also unclear what fraction of the three gigatons plants are taking up due to rising levels of CO₂.
Australia is now undergoing its third great wave of population growth, putting pressure on infrastructure, services and the environment. During the past two waves of growth, in the late-19th and mid-20th centuries, cities implemented visionary responses. It’s largely because of these past phases of planning and investment that our cities have until now been able to sustain their liveability and a reasonably healthy natural environment.
A third wave of planning and investment in open space and green infrastructure is now needed to underpin liveability as our cities grow. The past offers important lessons about what made Melbourne, in particular, so liveable.
Can we repeat the leadership of yesterday?
In the early 19th century, European settlers ignored and displaced the Indigenous knowledge and connections with country. What grew in their place were initially little more than shambolic frontier towns.
In the Port Phillip colony, the gold rush, the subsequent population and property booms and the lack of city services led to Melbourne gaining an international reputation as “Smellbourne”.
But then, over several decades, visionary plans set aside a great, green arc of parklands and tree-lined boulevards around the city grid.
Melbourne constructed one of the world’s earliest sewerage systems. The forested headwaters of the Yarra River were reserved for water supply. Melbourne is today one of a handful of major cities in the world drawing its natural water supplies from closed catchments.
And so, together with profound social and cultural changes, the shambolic frontier town transformed into “Marvellous Melbourne”. Sydney and Australia’s other capital cities followed similar trajectories.
Then came the world wars and intervening Great Depression. These were times of austerity and sacrifice. Remarkably little investment in open space and green infrastructure occurred over these decades.
The 1956 Melbourne Olympics was perhaps the event that signalled the awakening from that somewhat bleak period. It was again time for optimism and vision, with the post-war population boom well under way.
The 1954 Melbourne Metropolitan Planning Scheme reflected this growing optimism and highlighted the potential for a network of open spaces across the rapidly expanding city. But it took time to build momentum for its implementation.
By the 1970s sprawling development had virtually doubled the metropolitan area of Melbourne. Services such as the sewerage system had not kept up. The Yarra and other waterways and Port Phillip Bay were becoming grossly polluted. There was community pressure to tackle pollution caused by industry and unsewered suburbs.
The city’s planners revived the earlier vision for Melbourne’s open space network, along with the idea of green wedges and development corridors. Greater prosperity and community expectation secured the investment needed to deliver it.
The 1971 metropolitan plan identified open-space corridors for waterways including the Yarra. Land began to be acquired to build this green network and the trail systems that connect it. Victoria became known as the “Garden State” in the 1970s.
This period stands out as the city’s second great wave of visionary planning and investment. It created the wonderful legacy of a world-class network of open space, much of it around waterways and Port Phillip Bay.
Where to today?
Sustaining or improving urban liveability is a massive challenge. It calls for a new vision and a commitment by governments to deliver it over many decades. Do we have policies and institutions capable of doing this?
Rather than “shaping” our cities, many state institutions are dominated by cost and efficiency goals that drive a “city servicing” mindset.
Melbourne, for instance, is in danger of exhausting the legacy of the last “city shaping” phase of visionary planning and investment. This all but ended in the 1980s.
By 1992, the Melbourne and Metropolitan Board of Works had been abolished. It once had responsibility for town planning, parks, waterways and floodplain management as well as water and sewerage services. It used the Metropolitan Improvement Fund (raised from city-wide property levies) to plan and deliver the city’s green infrastructure, including land acquisitions.
Where is the equivalent capability today? Our practitioners have the knowledge, skills and understanding to better plan for complex city needs, but this is not enough to shape a better future for coming generations. Without a vision and effective policies and institutions to deliver it, we risk ad hoc and wasteful decision-making and investment. The result will be poorer community well-being and less economic prosperity.
The entrenched cost-efficiency or “city servicing” mindset is an all-too-narrow and short-term policy setting in an era of unprecedented urban population growth.
Expanding suburban fringes will lack amenity and a healthy environment, which may entrench disadvantage. Existing suburbs also need to improve quality, access and connectivity of public open space.
Green streetscapes, open space and tree cover are important for amenity. This includes countering urban heat in a warming climate. Co-ordinated investment in green infrastructure can also unlock new economic opportunities for our cities.
But, as the past has shown, little will happen without an effective city-shaping capability. Significant policy and institutional reforms, guided by a new vision, are essential to ensure a healthy environment, community well-being and the liveability and prosperity of our cities for decades to come.
Alternatively, we may find ourselves tumbling down the ranks of world’s most liveable cities. Our best and brightest will be drawn to greener pastures while the world asks in astonishment, “How did they let that happen?”
Global greenhouse emissions from fossil fuels and industry are on track to grow by 2% in 2017, reaching a new record high of 37 billion tonnes of carbon dioxide, according to the 2017 Global Carbon Budget, released today.
The rise follows a remarkable three-year period during which global CO₂ emissions barely grew, despite strong global economic growth.
But this year’s figures suggest that the keenly anticipated global peak in emissions – after which greenhouse emissions would ultimately begin to decline – has yet to arrive.
The Global Carbon Budget, now in its 12th year, brings together scientists and climate data from around the world to develop the most complete picture available of global greenhouse gas emissions.
In a series of threepapers, the Global Carbon Project’s 2017 report card assesses changes in Earth’s sources and sinks of CO₂, both natural and human-induced. All excess CO₂ remaining in the atmosphere leads to global warming.
We believe society is unlikely to return to the high emissions growth rates of recent decades, given continued improvements in energy efficiency and rapid growth in low-carbon energies. Nevertheless, our results are a reminder that there is no room for complacency if we are to meet the goals of the Paris Agreement, which calls for temperatures to be stabilised at “well below 2℃ above pre-industrial levels”. This requires net zero global emissions soon after 2050.
The most significant factor in the resumption of global emissions growth is the projected 3.5% increase in China’s emissions. This is the result of higher energy demand, particularly from the industrial sector, along with a decline in hydro power use because of below-average rainfall. China’s coal consumption grew by 3%, while oil (5%) and gas (12%) continued rising. The 2017 growth may result from economic stimulus from the Chinese government, and may not continue in the years ahead.
The United States and Europe, the second and third top emitters, continued their decade-long decline in emissions, but at a reduced pace in 2017.
For the US, the slowdown comes from a decline in the use of natural gas because of higher prices, with the loss of its market share taken by renewables and to a lesser extent coal. Importantly, 2017 will be the first time in five years that US coal consumption is projected to rise slightly (by about 0.5%).
The EU has now had three years (including 2017) with little or no decline in emissions, as declines in coal consumption have been offset by growth in oil and gas.
Unexpectedly, India’s CO₂ emissions will grow only about 2% this year, compared with an average 6% per year over the past decade. This reduced growth rate is likely to be short-lived, as it was linked to reduced exports, lower consumer demand, and a temporary fall in currency circulation attributable to demonetisation late in 2016.
Yet despite this year’s uptick, economies are now decarbonising with a momentum that was difficult to imagine just a decade ago. There are now 22 countries, for example, for which CO₂ emissions have declined over the past decade while their economies have continued to grow.
Concerns have been raised in the past about countries simply moving their emissions outside their borders. But since 2007, the total emissions outsourced by countries with emissions targets under the Kyoto Protocol (that is, developed countries, including the US) has declined.
This suggests that the downward trends in emissions of the past decade are driven by real changes to economies and energy systems, and not just to offshoring emissions.
Other countries, such as Russia, Mexico, Japan, and Australia have shown more recent signs of slowdowns, flat growth, and somewhat volatile emissions trajectories as they pursue a range of different climate and energy policies in recent years.
Still, the pressure is on. In 101 countries, representing 50% of global CO₂ emissions, emissions increased as economies grew. Many of these countries will be pursuing economic development for years to come.
A peek into the future
During the three-year emissions “plateau” – and specifically in 2015-16 – the accumulation of CO₂ in the atmosphere grew at a record high that had not previously been observed in the half-century for which measurements exist.
It is well known that during El Niño years such as 2015-16, when global temperatures are higher, the capacity of terrestrial ecosystems to take up CO₂ (the “land sink”) diminishes, and atmospheric CO₂ growth increases as a result.
This event illustrates the sensitivity of natural systems to global warming. Although a hot El Niño might not be the same as a sustained warmer climate, it nevertheless serves as a warning of the global warming in store, and underscores the importance of continuing to monitor changes in the Earth system.
No room for complacency
There is no doubt that progress has been made in decoupling economic activity from CO₂ emissions. A number of central and northern European countries and the US have shown how it is indeed possible to grow an economy while reducing emissions.
Other positive signs from our analysis include the 14% per year growth of global renewable energy (largely solar and wind) – albeit from a low base – and the fact that global coal consumption is still below its 2014 peak.
These trends, and the resolute commitment of many countries to make the Paris Agreement a success, suggest that CO₂ emissions may not return to the high-growth rates experienced in the 2000s. However, an actual decline in global emissions might still be beyond our immediate reach, especially given projections for stronger economic growth in 2018.
To stabilise our climate at well below 2℃ of global warming, the elusive peak in global emissions needs to be reached as soon as possible, before quickly setting into motion the great decline in emissions needed to reach zero net emissions by around 2050.
Despite robust global economic growth over the past two years, worldwide carbon emissions from fossil fuels grew very little in 2014, and might even fall this year.
A report released today by the Global Carbon Project has found that fossil fuel emissions of carbon dioxide grew by only 0.6% in 2014, breaking with the fast emissions growth of 2-3% per year since early 2000s. Even more unexpectedly, emissions are projected to decline slightly in 2015 with continuation of global economic growth above 3% in Gross Domestic Product.
This is the first two-year period in a multi-decade record where the global economy shows clear signs of decoupling from fossil fuel emissions. In the past, every single break or decline in the growth of carbon emissions was directly correlated with a downturn in the global or regional economy.
This time is different.
However, it is quite unlikely that 2015 is the much-sought-after global peak in emissions which will lead us down the decarbonisation path required to stabilise the climate.
In a separate paper published today in Nature Climate Change, we look in more detail at the possibility of reaching global peak emissions.
What caused it?
The principal cause of this unexpected lack of growth in emissions is the slowdown in the production and consumption of coal-based energy in China in 2014, followed by a decline in 2015.
This has taken China’s emissions growth from close to double digits during the past decade to an extraordinary low of 1.2% growth in 2014 and an unexpected decline by about 4% projected for 2015.
Although China is only responsible for 27% of global emissions, it has dominated the growth in global emissions since early 2000s. Therefore, a slowdown in China’s emissions has an immediate global impact.
Further adding to this main cause, emissions from industrialised economies, including Australia, Europe and the United States, have declined by 1.3% per year on average over the past decade, partially supported by extraordinary growth of renewable energy sources.
Have we reached global peak emissions?
Most likely not. One key uncertainty in answering this question is the future of coal in China. But China is pushing to achieve peak carbon consumption as early as possible (and emissions by 2030), and to phase out the dirtiest types of coal from the nation’s energy mix, largely in response to a pollution crisis affecting many of its large urban areas. It is well within the possibilities that growth in coal emissions in China will not resume any time soon, and certainly not at the fast pace of the previous decade.
A strong basis for this assessment is the remarkable growth in non-fossil fuel energy sources such as hydro, nuclear and renewables. These accounted for more than half of the growth in new energy in 2014, with a very similar mix during the first three-quarters of this year. Such structural changes, if continued, could bring China’s peak emissions much earlier than anyone is anticipating and certainly well before 2030.
Although it is unlikely that we have reached global peak emissions, it is very likely that 2015 marks a new era of slower growth in fossil fuel emissions. This is perhaps the first sign of a looming peak on a not-too-distant horizon.
This might well be the future. But models used for such analysis were not that different from those that completely missed the very rapid rise of the Chinese economy in the decade of 2000 and perhaps now its rapid decarbonisation.
However, China is not alone in this game. Industrialised countries plus China, accounting for half of global fossil fuel emissions, have pledged to reduce or stabilise emissions absolutely by 2030.
But the other half belongs to less-developed nations whose pledges do not include absolute emission reductions but departures from business-as-usual scenarios (meaning emissions can increase, but not as fast). This emphasises the disproportionate importance of international climate finances required to help that “other” half of the emissions to peak and join the decline of the rest.
2015 has been an extraordinary year, and not just because of China. Emissions from Australia, Europe, Japan and Russia have all come down as part of longer or more recent trends. Installed wind capacity reached 51 gigawatts in 2014, an amount greater than the total global wind capacity just a decade ago. Solar capacity is 50 times bigger than it was ten years ago.
And emissions from land-use change, albeit with large uncertainties and high emissions from Indonesian fires this year, have been on a declining trend for over a decade. These trends are not stopping here.
Yet the current emissions path is not consistent with stabilising the climate at a level below 2℃ global warming.
If we maintain the level of 2015 emissions, the remaining carbon budget before setting the earth on a path that exceeds 2℃ is less than 30 years away, unless we bet on unproven negative emissions technologies to remove carbon from the atmosphere later in the century.
But 2015 is a historic year to galvanise further action. The trends in emissions are favourable, and countries have the opportunity to negotiate significantly higher levels of ambition to decouple economic growth from emissions.
Pep Canadell, CSIRO Scientist, and Executive Director of Global Carbon Project, CSIRO