It seems inevitable now that global temperatures will reach or exceed the +1`.5 Celsius above pre-industrial levels by 2050, the deadline to avoid any increase beyond this by the 2015 Paris Agreement.

In the year to the end of June 2024, global temperatures surpassed that threshold for 12 consecutive months and the month itself was the hottest June on record, sitting right on the +1.5 Celsius. In fact, the period 16-24 June, was the first seven consecutive days on which the threshold was passed.

It all sounds pretty gloomy and anyone with the slightest concern about what this means is wondering what the future holds for global biodiversity, of which humans are a part and on which they are directly for health, prosperity and, ultimately, survival.

The hotly debated issue remains: what is our contribution to climate change and what can we realistically expect we can do about it? This “anthropocene question” and the way we answer it will detemine the quality and capacity of future generations to live in it healthily and peacefully.

The anthropocene period follows the holocene that lasted from the end of the ice age approximately 11,700 years ago to around 70 years ago. The holocene was a golden era of almost perfect climatic conditions for optimal biodiversity.

The anthropocene period, as the name suggests, is defined by human influence on Earth’s biosphere. It is the first epoch in which a single species has had the power to substantially determine the future conditions under which all life will exist.

The kick-off date for the anthropocene is debated, but generally accepted to be in the decade from 1950, when the impacts of the industrial revolution in the latter part of the 19th Century were becoming clearly measurable.

Time to ditch climate denial

Those who believe that human activity is a significant contributor to climate change, including most of the world’s leading scientists, accuse those on the other side of the debate with climate denial.

As always, this is a generalisation that is not true of everyone. Some accept that climate is changing and global temperatures rising, but debate the contribution of human activity to this, particularly carbon emissions from industry, agriculture and deforestation.

They point to natural cycles over millennia that have changed climate and biodiversity and claim what we’re seeing is another natural shift. So it’s not climate denial in play, it’s disagreement over the human drivers of it. There are of course absolute climate deniers at the extreme, who interpret a cold winter as evidence that everything is normal, but we can discount their warblings as beyond the realms of serious debate.

Let us accept on both sides that climate change is self-evident, both scientifically and experientially, and focus the debate on the anthropocene question.

Human contribution to climate change

Atmospheric carbon levels are increasing, currently around 420 parts per million (ppm). Those arguing that human activity has had little part to play in this point to previous periods when carbon levels have been this high. They’re correct, they were this high around 14 million years ago and even higher 16 million years ago, before the Earth’s climate began to cool.*

Some argue that periods of the Miocene stretching from 16 million to 23 million years ago, featured rich biodiversity fuelled by high carbon levels and a much warmer climate, concluding that higher levels of atmospheric carbon are positive for life.

Most studies of deep climate history extending over millions of years indicate that every doubling of atmospheric greenhouse gas levels results in global temperature increases of between 1.5 and 4.5 Celsius. Since 1700, these levels have moved from approximately 280 ppm to the current 420 ppm.

This graph is a fine illustration of the alignment of the most dramatic increase in atmospheric carbon dioxide levels with the start of the anthropocene period. The increase in levels since the 1700s has mostly occurred since the 1950s.

For some, the hyperbolic rise in atmospheric carbon dioxide is insufficient evidence of human contributions to it. They argue that this could correlate with natural cycles, often referencing climate change induced by the Milankovitch cycles, which describe slight changes in the Earth’s orbit around the Sun. These do cause substantial changes in climate over times scales of between 26,000 and 100,000 years.+ They do not drive carbon dioxide levels and climate change over a half century.

Consider this. In the absence of human-induced greenhouse gas emissions, what sort of shifts in the natural biodiversity balance would be required to accelerate the increase in carbon dioxide levels at the rate seen since the 1950s?

Our impact on biodiversity loss is beyond question

Even if human-generated atmospheric emissions were not contributing to climate change, an idea to which I do not subscribe, our impact on terrestrial and marine biodiversity is removing many of the most powerful mitigations against the obvious outcomes of a climate out of control - more fierce and frequent storms, sea level rise and surges, horrendous wildfires and health impacts, including deaths, from heat exposure.

As we ponder this question, we need to think about the increase in greenhouse gases, particularly carbon dioxide in the context of both human environmental outputs and inputs.

The outputs reference the things most hotly debated - emissions created primarily as we burn fossil fuels to power industry, homes and lifestyle pursuits. On the flipside, there is human impact on the natural habitats that, if left alone, could help mitigate those outputs.

The Intergovernmental Science Policy Platform on Biodiversity and Ecosystem Services (IPBES) in 2021 noted the five primary drivers of biodiversity loss were: land use change, direct exploitation of wild species, climate change, invasive alien species, and pollution.^^

For the sake of the climate sceptics, let’s ignore the human influence on climate change. It leaves four factors that are undeniably human-induced, thanks to the shifts and demands of the demographics and economics that are societal highway markers on our march into the future. Whether these are the sole, appropriate measures of success is a debate for another time.

There is an inextricable link between biodiversity loss and the changing climate. What we do with ecosystems alters carbon cycles, water exchange and nitrogen circulation. For example, the Amazon Basin, long considered a net absorber of carbon dioxide is now a net emitter due to deforestation and land degradation.

In 2021, 141 countries signed up to halt or reverse forest loss by 2030 under the Glasgow Leader’s Declaration on Forests and Land Use. This at the end of two decades in which forest loss, particularly in the tropics has remained stubbornly high.

These and extensive loss of Boreal forests in Russia represent substantial loss of terrestrial forest capacity to absorb and sequester carbon.

Equally important is arresting the decline of marine habitats - mangroves and seagrasses - which can absorb carbon at between 30 and 50 times the rate of equal areas of terrestrial forests.^

Accepting this, there is considerable work under way to model the future of these marine habitats. While in recent years, the rate of mangrove loss has slowed, seagrasses are very subsceptable to sea water temperature changes and acidification.

“Coastal development and other damage since the 1800s has cost us about 25 percent of all salt marshes worldwide. We’ve lost 30-50 percent of all mangrove forests since the 1940s. Just since the 1990s, we’ve lost 50 percent of all seagrass meadows. We continue to lose mangroves at a rate that could be as much as 3 percent per year, salt marshes at 1-2 percent per year, and sea grasses at 7 percent per year.”

climate.gov, 2022 

Human incursion into natural habitat is stripping the Earth’s capacity to mitigate against and adapt to climate changes. For some, the results of this are and will be catastrophic.

The evidence of this is not only experiential and even existential for some, but is also appearing in the the national accounts of states and nations faced with community restoration in the wake of fires, floods and tempests. It is reflected in our own property insurance premiums as climate change is built into the risk calculations of the global insurance industry. For people in the most exposed locations, this tranlates into higher premiums and possibly no protection at all.

The final nail - the rate of change

Even scientists agree that climate modelling is imperfect. The evidence upon which science builds its case for capping carbon emissions is incomplete:

“The Miocene may be the best available analog for our future Earth under anthropogenic climate change. By studying it, many lessons can be learned, about for example the cause and consequences of highly elevated temperatures such as occurred during the MCO, and about the tipping zone for many climate subsystems (mostly occurring in the late Miocene). Improved understanding of how the Earth system operates under varying background conditions may enable us to answer such important questions as whether highly elevated temperatures can be achieved at relatively moderate pCO2, a particularly pertinent question as we enter uncharted territory of elevated pCO2 already at present.”

Source: The Miocene: The Future of the Past***

Nonetheless, the climate is changing. A mass extinction is looming with an estimated one million species under some level of threat.

Yes, major climatic shifts have occurred before. Nature has adapted. Species have come and gone. However, species adaption and survival has usually been enabled by a fairly gradual rate of climatic change over millennia.

The outstanding example of rapid and catastrophic climate change was approximately 66 million years ago when an asteroid strike near what is now the Yucatan Peninsula in the Gulf of Mexico led to rapid global warming, reduced sunlight, devastated plant life and, ultimately, the demise of around 70% of Earth’s species, including the dinosaurs.

Human activity since the industrial revolution from the mid-18th Century is accelerating change to a point where there is no time for adaptation to changed temperatures, acidification and natural cycles. Habitat and species that are very specialised, localised, even geographically isolated, are most vulnerable - unable to travel to more accommodating climes.

The debate and advocacy around human influence is relevant only to those who are prepared to surrender the future due to unwillingness to adjust their consumption, wealth expectations or behaviours to reduce their environmental footprint. Those who prefer to maintain the status quo and debunk climate modelling are ignoring the one thing that is evident: all models that examine the connection between climate and biodiversity over millennia confirm that the climate changes cause complex and irreversible changes to life on Earth.***

The anthropocene question has become a distraction. It has been made obsolete as events have overtaken it and the window of opportunity for nature-positive action has started to close.

We need positive action on climate and biodiversity, a new construct for living as part of rather than in conflict with nature, in order to meet our responsibilities for the health, wellbeing and, yes, even prosperity of future generations.

*Columbia University Climate School, A New 66 Million-Year History of Carbon Dioxide Offers Little Comfort for Today, Kevin Krajick, 2023

**Atmospheric CO2 data from NOAA and ETHZ. CO2 emissions data from Our World in Data and the Global Carbon Project. 

+ https://earthathome.org/quick-faqs/are-orbital-changes-causing-global-warming/

^ https://www.dcceew.gov.au/environment/marine/coastal-blue-carbon-ecosystems

^^ https://online.ucpress.edu/currenthistory/article/120/829/295/118794/Climate-Change-and-Biodiversity-LossTwo-Sides-of

***https://www.researchgate.net/publication/347960864_The_Miocene_The_Future_of_the_Past. Some climatologists have undertaken research that suggests atmospheric carbon dioxide levels are decoupled from climate change and that, in fact, CO2 levels can move in the opposite direction of average global temperatures. They argue that temperature rises can increase CO2 levels rather than the other way around. Here is one such paper: https://www.scirp.org/journal/paperinformation?paperid=131993