Gesellschaft Deutscher Chemiker
Anonymous

Anonymous

Keine Benachrichtigungen
Sie haben noch keine Lesezeichen
Abmelden

Climate change

Reasons, requirements, and realities

Von Wiley-VCH zur Verfügung gestellt

A look at the challenges in limiting global warming, progress made at 26th UN Climate Change Conference of the Parties (COP26) in Glasgow, and what more chemistry can contribute.

Global warming is being driven by human activities generating atmospheric greenhouse gases (GHGs). As the resulting climate effects intensify, there will be long-term consequences for the habitability of large regions of the planet’s surface. Achieving stability and sustaining the present type of climate requires limiting the temperature increase to not more than 1.5°C above pre-industrial levels.1) The 2015 Paris Agreement on climate change committed governments to limiting warming to well below 2°C above pre-industrial levels and to “pursuing efforts” to prevent more than 1.5°C of warming. However, human-induced warming has already reached about 1.1°C above pre-industrial levels and, at the present rate, global temperatures would reach 1.5°C around 2040 and 2.7°C by the end of the century.2) The COP26 conference3) in Glasgow in November 2021 was framed as the last opportunity for the world to correct its course and credibly retain the 1.5–2.0oC goal.4)

Grafik: vektorMine/Adobe Stock

Greenhouse gases

Unlike the main constituents of air, CO2 absorbs the infrared energy produced by sunlight reflecting off the Earth’s surface, which would otherwise escape back into space. The CO2 then re-radiates the infrared energy in all directions, and much of the energy remains on Earth, leading to warming. For at least the last 800,000 years, the level of CO2 in the atmosphere oscillated in a range from about 180 ppm up to 300 ppm.5) However, since the mid-20th century, the level has been increasing rapidly, surpassing 400 ppm in 2013 and reaching 412.4 ppm in 2020. This atmospheric CO2 level was last seen more than three million years ago,6) when the temperature was 2°–3°C higher than during our pre-industrial era and the sea level was 15–25 metres higher than today.

Three gases make up most of the GHG emissions:7)

CO2 generated by burning carbon-containing materials causes three-quarters of the total man-made GHG effect. Furthermore, the manufacture of cement powder from mixtures containing CaCO3 liberates CO2 both from the generation of heat from combustion of fossil fuels and from the high-temperature decomposition of the CaCO3. Cement production accounts for 8% of the world’s total annual emissions of CO2.8) Together, burning fossil fuels for energy and producing cement emit over 36 Bn tonnes/year of CO2 globally, out of the annual total of around 43 Bn tonnes.

CH4 accounts for 17% of the total GHG effect. It arises from three main sources: about 20% from the bacterial decomposition of organic waste, 36% from leakages from the production and use of fossil fuels, and 44% from agriculture.9) Nearly three-quarters of the agriculture-derived CH4 is produced by fermentation of food being digested by animals, and nearly one-quarter through the action of microbes in fields – about half of this in flooded rice paddies.10) Methane’s role in global warming is especially important because it is about 80 times more powerful than CO2 as a GHG, but it is a relatively short-lived, breaking down after an average of around 12 years in the atmosphere while CO2 may persist for thousands of years.11) Thus, immediate major reductions in the amount of CH4 being emitted can yield significant near-term reductions in the global warming potential of the atmosphere.

N2O sources in the atmosphere include some industrial emission, but mostly agriculture, where it is formed by the action of microbes on nitrogen compounds in fertilised soils and animal manure. Weight-for-weight, N2O warms the atmosphere about 265 times as much as CO2 and it has an average atmospheric lifetime of 121 years. Overall, it represents about 6% of the greenhouse warming capacity of the atmosphere.11)

Science solutions are available, but COP26 made limited progress

To limit climate change, effort is necessary in two major areas. One is to end the destruction of forests that help retain already locked-in carbon and remove carbon dioxide present in the atmosphere. In the Glasgow Leaders’ Declaration on Forests and Land Use,12) 91% of the world’s forests were covered by a pledge from 137 countries to halt and reverse forest loss and land degradation by 2030. However, there are fears that implementation of this Declaration may be weak: Its forerunner, the 2014 New York Declaration, had failed to slow deforestation.13)

The complementary critical step is to cease emitting GHGs into the atmosphere. This requires a range of interventions across all the major sectors and activities that presently generate GHG emissions and, in each area, using different, overlapping approaches that will have short-, medium- and long-term effects. The final outcome document from COP26, the Glasgow Climate Pact,14) made some progress, but while it reaffirms the 2015 Paris Agreement goal to pursue efforts to achieve the 1.5oC global warming limit, the urging15) to “keep 1.5 alive” did not result in commitments that would deliver this result.16) Many of the largest economies, including China, the European Union (EU), and the USA, announced targets of net zero emissions by 2050, while India unveiled plans for the first time for achieving net zero emissions – but 20 years later, by 2070. Estimates suggest that, if all the pledges made in Glasgow were fully met, a temperature rise limited to 1.8–1.9oC is feasible,15a) but it is widely expected that implementation will fall significantly short of this.

Energy

Eliminating CO2 emissions will require largely, if not completely, ceasing to burn fossil fuels, only continuing their consumption when the CO2 produced is captured and locked into long-term storage forms or other uses where it is not released into the atmosphere. In 2019, oil provided about 39% of the energy from fossil fuels, coal 32%, and gas 29%.17) Coal is currently the most heavily polluting of the major fossil fuels since, in addition to CO2, combustion emits sulphur oxides from sulphur impurities it contains as well fine particulate matter that adds to local environmental contamination and health hazards, and it leaves ash to be disposed of. Reducing coal consumption in favour of natural gas (mainly CH4) provides immediate benefits in terms of reducing emissions of coal-derived pollutants and GHGs (as seen, e.g., in Germany, the UK and the USA). However, natural gas, even when completely combusted, still releases about 50–60% of CO2 emissions compared to coal. Moreover, leakages of CH4 always occur during extraction, transport, and combustion. Methane’s much higher global warming potential means that the leakage rate must be kept below 3–5% (the exact break-even point depends18) on what type of coal is being substituted); otherwise there is still a net increase in the greenhouse effect.

Over 100 countries attending COP26 agreed to reduce CH4 emissions by 30% by 2030. The USA’s own blueprint19) for achieving this emphasised action on several fronts, including: cutting leakages and emissions from the oil and gas sector (the largest source), reducing CH4 emissions by remediating abandoned coal mines, reducing food loss and waste that serves as a major contributor to landfill CH4 emissions, and initiating an incentive-based “climate-smart” agriculture programme, in particular with attention to alternative manure management systems. Canada announced that it would cut CH4 emissions from its large oil and gas industry by 75% by 2030. According to the International Energy Agency’s Net Zero by 2050 Roadmap,20) that is how fast overall global CH4 emissions will need to be cut if the world is to reach net zero by mid-century.

Alternatives to fossil fuel combustion for the long term include geothermal, hydroelectric, nuclear, solar, wind, and wave sources of energy. All these options avoid CO2 emissions at the point of energy generation, but each presents a range of other challenges – including technical, economic, environmental, social, and political – that need to be worked through. Moreover, each method requires specific hardware. This may range from large constructions (e.g., dams, turbines) to sophisticated devices (e.g., solar cells and panels) – all of which, on a scale that would be needed for global effect, would require massively increased operations for mining, refining, transport, material transformations, assembly and installation, maintenance, and renewal.21)

The Glasgow Climate Pact final text calls for rapid scale-up of the deployment of clean power generation and energy efficiency measures, including “accelerating efforts towards the phase-down of unabated coal power and inefficient fossil fuel subsidies”. While including a reference to coal for the first time, a late intervention led by India and China watered down an earlier draft text that had called for the phase-out of coal.22)

Transport

Developing alternative mobile forms of energy is the core challenge in eliminating GHG emissions in the transport sector. Transport presently accounts for around one-fifth of global CO2 emissions, with the largest three contributors being passenger cars, trucks, and aviation.23) One approach to the replacement of oil products for the internal combustion engine involves the storage of energy in batteries for electric vehicles. The technical challenges of increasing the power of batteries (currently based on Li) and reducing charging time are gradually being overcome, and a number of countries are setting target dates within the next one to two decades for phasing out oil-based in favour of electric vehicles. As with energy production at fixed locations, the question of the sourcing and turnover of the necessary materials on a global scale needs to be carefully considered. For example, the restricted geographical locations of known, accessible supplies of Li have led to concerns about the potential to satisfy projected world demands.21) Efforts to meet the challenge include developing the recycling24) of Li batteries, while alternative Li sources (e.g., seawater extraction25)) and replacement materials (e.g., Al, Mg, Na, Zn) are being explored.

An alternative is the replacement of oil-based fuels with substances that can be carried in the vehicle and used to create the motive force required. Options include the use of H2 fuel cells, or combusting materials such as H2 without liberating pollutants. However, H2 is currently derived from CH4, with co-generation of CO2, and it would need to be made instead by splitting water using energy from solar or other non-carbon-based sources. Also, transport of H2 presents dangers of leakages, fires, and explosions. Recently, there has been rising interest in the possible use of NH3 as a fuel.26) It can also be burned in a combustion engine, producing N2 and H2O, and has a higher energy content than H2. Ammonia is liquified at a much higher temperature (–33oC) than H2 (–253oC) but is not as highly flammable. However, NH3 is toxic by inhalation and acts as a severe respiratory tract irritant. Furthermore, the Haber-Bosch industrial process used for the last 100 years to manufacture NH3 itself emits very large amounts of CO2, and new “green NH3” technologies27) are needed to make this a carbon-free energy alternative.

Clean technologies

Across the political negotiations and agreements on individual targets for reducing GHG emissions and preserving and restoring forests and soils, there was recognition that technology would play a crucial role. More than 40 countries attending COP26, including Australia, China, the EU, India, Turkey, and the USA, agreed on a UK-led plan, the “Breakthrough Agenda”,28) to speed up affordable and clean technology worldwide by 2030. Five initial goals set out were:

Power: Clean power becomes the most affordable and reliable option worldwide.

Road transport: Zero-emission vehicles become the new normal and are accessible, affordable, and sustainable in all regions.

Steel: Near-zero emission steel is the preferred choice in global markets, with efficient use and near-zero emission steel production established and growing in all regions.

Hydrogen: The aim is for affordable renewable and low-carbon hydrogen to be globally available.

Agriculture: Climate-resilient, sustainable agriculture becomes the most attractive and widely adopted option for farmers everywhere.

While investments would be needed to make these breakthroughs, it was projected that they could create 20 million new jobs globally and add over 16 trillion U. S. Dollar across both emerging and advanced economies.

Outlook

Ending GHG emissions will require massive efforts by all countries and carries implications for many aspects of economies, transport, food production, and much else. Consequently, the decisions taken in COP26 and to be taken in future climate negotiations, while needing to be rooted in sound science and technology, are all ultimately political. For greatest impact, chemistry must therefore be active in both science and policy-shaping.

In a nutshell

Chemical processes are at the core of the anthropogenic production of atmospheric greenhouse gases (GHGs) in industry, agriculture and the environment.

Chemistry must therefore be central to reaching the objective of limiting global warming, through helping clean up the atmosphere and develop smarter materials, technologies and processes that prevent GHG release.

Efforts in these areas are under way, but urgently need to be intensified.

The authors

The article was written by members of Chemists for Sustainability (C4S), an action group of the International Organization for Chemical Sciences in Development (IOCD). C4S has received support from GDCh and Royal Society of Chemistry. Authors are: Henning Hopf (right), former President of the German Chemical Society, Alain Krief (second from left), former Executive Director of the IOCD, Goverdhan Mehta (left), University of Hyderabad, India; Stephen A. Matlin, Visiting Professor, Imperial College London, UK and Senior Fellow in the Global Health Centre, Geneva, Switzerland.

Bildung + Gesellschaft

18

Überprüfung Ihres Anmeldestatus ...

Wenn Sie ein registrierter Benutzer sind, zeigen wir in Kürze den vollständigen Artikel.