Climate change: the big picture is being missed

Since 1970 there has been an overall decline of 60% in the sizes of vertebrate populations around the world, and within each vertebrate class (mammals, birds, reptiles, amphibians, fish) at least two thirds of the losses are still being caused by habitat loss and degradation together with species overexploitation. The tropics are hardest hit, particularly in South and Central America (including the Caribbean) where the decline has been over 80%.

Freshwater ecosystems are under exceptional pressure and some major rivers are so heavily used that for most of the time they peter out before reaching the sea. Agriculture, in one form or another, accounts for some 70% of water withdrawal and water tables in many places are falling drastically as a result of pumping groundwater. But people make multiple demands on rivers and wetlands and the local consequences of urbanization can also be painfully obvious in polluted waterways near built-up areas.

Perhaps more surprisingly, water-worn sand has become a precious commodity, mainly for making concrete and largely to meet a demand driven by burgeoning urbanization. China, in the years between 2011 and 2014,is reported to have used more concrete than did the United States during all of the 20th century.It is not clear whether total demand exceeds global supply but there are certainly regional scarcities to which the world's tallest building stands testimony. Concrete for the Burj Khalifain Dubai was made from sand and gravel imported from Australia. The rounded, wind-blown grains of desert sands are not suitable for concrete. Coastal sands do meet the required standards but the need to wash out salt increases the cost.

Sand mining and dredging are poorly regulated and frequently illegal but 'sand mafias' are powerful enough to bribe and intimidate their way to huge profits. River beds are scoured and sandbanks and beaches are trucked and shipped away with no regard for natural ecosystems, coastal protection or communities of fishing folk whose livelihoods are destroyed.

In ordinary concrete the sand is bound by cement consisting largely of crushed clinker. The clinker is made by roasting limestone with clay in very hot kilns, and the process emits CO₂ amounting to at least half the weight of the clinker it produces. That is regardless of the source of energy used to power the kilns.

Sustainable development

At a United Nations summit, held in New York in 2015, world leaders tried to see the bigger picture and pledged to take action, simultaneously, on a broad range of environmental, economic and social issues, including climate. The leaders signed up to a package of 17 Sustainable Development Goals (SDGs) incorporating a total of 169 'targets' to be reached by 2030.

Now, five years later and with a decade to go, it looks unlikely that many SDGs will be reached and the targets to protect climate and biodiversity have actually slipped further away. In September last year, the UN published a Global Sustainable Development Report prepared by an independent group of fifteen scientists. The report points out that adopting appropriate policies will require 'a profound and intentional departure from business as usual' - nothing short of a transformation of social, environmental and economic systems.

The 17 separate goals are not independent of each other so the scientists came up with half a dozen 'entry points' through which the goals can be approached in combinations that will best enable the countless interactions to be managed. On this basis, the climate, together with life on land and in water (SDGs 13–15) are lumped together in a single entry point called the 'global environmental commons'. The combination seems logical and it might be thought that actions to mitigate climate change would also benefit biodiversity. But, of course, it's complicated.

What do we want? When do we want it?

Coal-fired power generation accounts for 30% of all energy-related carbon dioxide emissions so electricity generation has become a prime target for climate activists - for whom a switch to renewable energy sources cannot come too soon.

Among the familiar renewables are solar, wind, and hydropower. Comparing their efficiency as energy sources involves doing life-cycle analyses so that the energy used in constructing, maintaining and decommissioning the plants is taken into account. Published analyses vary wildly because so many variables are involved and the analyses are not necessarily standardized. In the end, the most effective mix of energy sources will be largely determined by local geography. In general, however, the economic outlook favours renewables, not fossil fuels.

Environmental concerns are something else. Carbon dioxide is not released when wind and water spins turbines, or solar energy generates electricity, though fossil fuels may be used in manufacture, setup and end-of-life processes. Environmental damage from windfarms depends on where they are located. Trees may need to be cleared, access roads built and substantial excavations carried out for cable trenches and foundations; a single big turbine requires more than a thousand tonnes of concrete at its base. Depending on soil types and drainage patterns, ecological effects can be quite far-reaching.

Hydropower, as a threat to natural ecosystems, is in a category of its own. In Europe and the USA, between 1920 and 1970, thousands of dams were built for hydropower and they caused substantial ecological and social disruption. In those countries more dams have been removed than have been built in recent years. But sizeable portions of the globe are being transformed by a dam-building boom in developing countries.