Warming’s anthropogenic and is approaching irreversible tipping points

Researchers are sounding the alarm, predicting that the world is on a trajectory toward a tipping point marked by extinctions and unpredictable changes on a scale unprecedented since the retreat of the glaciers 12,000 years ago (Pappas, 2012). Professor Anthony Barnosky et al. (2012) from the University of California, Berkeley, along with 17 other scientists, caution that planet Earth may transform into a less hospitable abode for life. As per Barnosky et al. (2012), "There is a very high possibility that by the end of the century, the Earth is going to be a very different place. You can envision these changes as a fast period of adjustment where we get pushed through the eye of the needle. As we are going through the eye of the needle, that is when we see political strife, economic strife, war, and famine." The smooth curve in blue shows northern hemisphere temperatures over a period of 1000 years. Its uncertainty range is in light blue, which is overlaid with green dots showing a 30-year global average. The red curve shows the measured global mean temperature since the Industrial Revolution.

For decades, climate change deniers have vigorously attempted to discredit the hockey stick graph (Graph 7.2) developed by Michael Mann and his colleagues. However, in a remarkable turn of events, more than 25 years later, numerous independent reconstructions of past temperature changes have emerged, all validating Mann and his colleagues' original findings. Recently, during his acceptance inaugural speech for the Humanist of the Year award by the American Humanist Association (AHA), Michael Mann had eloquently articulated the significance of these validations. He had highlighted that the latest studies suggest that the warming of our planet in recent decades is unparalleled in tens of thousands and even hundreds of thousands of years (Mann, 2023).

This emphasizes the unprecedented nature of the situation we find ourselves in today, as we are involved in an uncontrolled and unparalleled experiment with the only planet we currently call home—a planet that sustains us and countless other life-forms. Mann and his colleagues have significantly contributed to our under- standing of the urgent need to address climate change and its consequences. As we continue to navigate the complexities of this global issue, Mann's words serve as a reminder of the critical importance of safeguarding our planet for the benefit of cur- rent and future generations and living systems on planet Earth.

Alan Buis (2011) predicts that by 2100, anthropogenic climate change will induce shifts in ecosystems and plant communities across almost half of Earth's land surface. This will result in nearly 40% of land-based ecosystems transitioning from one major ecological community type to another, such as forests, grasslands, or tundra. Scientists have been raising concerns about the ecological repercussions of global warming of even a few degrees. Should major greenhouse gas-emitting countries fail to drastically reduce their emissions and limit the global temperature increase to below 1.5 °C by 2050, all terrestrial ecosystems on planet Earth will be subjected to major transformations that will drastically alter the world's biomes. This will have far-reaching consequences for everything from water and food security to public health and biodiversity loss. Unchecked climate change could fundamentally transform our terrestrial ecosystems, posing immense risks to the diversity of our planet. It is likely to result in dramatic global landscape changes, equivalent to an ecological transformation occurring over one or two centuries, akin to the transformation that took place over 10-20 thousand years at the end of the last deglaciation period 21,000 years ago (E360 Digest, 2018). The changes in the atmosphere and oceans can profoundly impact the biosphere, the delicate layer of life on Earth that is intrinsically interwoven with the atmosphere and hydrosphere and provides the life-supporting matrix within which human societies exist. Yadvinder Malhi et al. (2020) posit that the degradation or restoration of parts of the biosphere will likely have regional or planetary consequences, including anthropo- genic greenhouse gas emissions, which drive both climate change and ocean acidification, increasingly threatening the viability and resilience of natural ecosystems and the human societies that depend upon them.

Cultivation of land through agriculture, along with millennia of deforestation, has potentially injected hundreds of billions of tons of carbon into Earth's atmosphere. As we transitioned into the industrial era, our reliance on carbon-laden sources of energy further exacerbated this issue. The combustion of coal and natural gas in power plants that illuminate our homes and the use of petroleum in various modes of transportation have collectively bolstered the net accumulation of carbon dioxide (C02) in the atmo- sphere. At present, an average person emits approximately 5 tons of carbon dioxide annually, a quarter of which will endure in the atmosphere for over a millennium (Hsiang et al., 2017). Greenhouse gases like CO: disrupt the planet's energy equilib- rium. According to Hsiang and Kopp (2018), the escalation of greenhouse gases in the atmosphere obstructs some of this reradiation, rechanneling energy back toward Earth. An increase of 1% in atmospheric C02 concentrations translates to roughly 27 trillion watts, or 0.05 watts per square meter. This is equivalent to the energy output of a Hiroshima-scale atomic bomb disseminating across Earth's surface every 2.3 s. The concept that anthropogenic activities could modify the climate goes back to nearly two centuries. Empirical studies conducted in the latter half of the twentieth century have cemented the understanding that human actions have been pivotal in reshaping the climate (Stocker et al., 2013; UGCRP. 2017). Given the weight of scientific evidence, the hypothesis positing no human influence on global climate has been unequivocally refuted (Hegerl et al., 2007).

Researchers have reviewed extensive studies on climate change, ecology, and Earth's tipping points, revealing thresholds that, when surpassed, can incite an environmental domino effect. Excessive pressure on the environment can catalyze these inflection points, triggering major global transitions (Barnosky et al., 2012). The most recent of such a transition has been the conclusion of the last glacial period when, within a span of 3000 years. Earth transitioned from being 30% ice-covered to its current near ice-free state. A substantial portion of the extinctions and ecological shifts occurred within a mere 1600 years. Between 1970 and 2010, our planet has experienced a staggering loss of 52% of its biodiversity, thereby heightening concerns about the revival of Earth's lost biodiversity (Lipton et al., 2018; Specktor, 2019). In the present day, human-induced alterations to the environment occur at a pace exceeding natural ones. The Industrial Revolution, instigated by a 35% increase in atmospheric carbon dioxide, has induced global temperature increases that outpace those observed in preindustrial times. Concurrently, humans have extensively modified 43% of Earth's land surface for urban and agricultural purposes, compared to the 30% land surface transition that occurred at the close of the last glacial period. With the human population burgeoning, exerting increasing pressure on existing resources (with a current population of eight billion), the consequences are challenging to predict, as these tipping points are propelling the planet into uncharted territories.

A departure from the current trajectory necessitates robust political determination and global collaboration. By 2025, human activities are projected to utilize 50% of Earth’s surface. With an inevitable population boom to nine billion by 2050, efficiency in resource utilization is crucial for sustainability. This necessitates more efficient energy consumption and production, a heightened focus on renewable resources, and an immediate imperative to conserve species and habitats for future generations. Scientists (Specktor, 2019; Pappas, 2012; Carrington, 2019) urge us to acknowledge that we are at a critical juncture. Should we opt for inertia, we risk encountering these tipping points and an unimaginable future dystopia for our descendants. Climate change is perceived as the foremost threat to our planet. It could intensify extreme weather events, precipitate droughts in some regions, destabilize rainfall patterns, accelerate glacial melting in the Himalayas and Antarctica, alter the global distribution of animals and diseases, and inundate low-lying areas due to rising sea levels (Lipton et al., 2018; Hausfather, 2017; Kolasi, 2017).

An alarming policy paper from an Australian think tank contends that the risks posed by climate change are more severe than generally anticipated (Specktor, 2019). This paper underscores that climate change presents a near-to-midterm existential threat to human civilization and that societal collapse by 2050 is a tangible risk if substantial mitigation efforts are not implemented in the ensuing decade. It warns that climate scientists have been overly conservative in their predictions about climate change’s impact on the planet in the near future. The ongoing climate crisis surpasses any previous human encounters in its magnitude and complexity. According to Hayhoe et al. (2018), global average temperature has escalated by about 1.8 °F from 1901 to 2016. As a result of the precarious shifts in climate and weather owing to the relatively small changes of one or two degrees in the planet’s average temperature, numerous global regions have experienced changes in rainfall patterns, culminating in more floods, droughts, and intense rain as well as more frequent and severe heat waves. The planet’s oceans, as well as the glaciers and ice caps in high mountainous regions and Antarctica, have witnessed significant alterations; oceans are warming and acidifying, glaciers and ice caps are melting rapidly, and sea levels are rising (Fleming et al., 2018). Climate scientists and researchers warn that when these and other adverse changes become more pronounced in the coming decades, they will pose formidable challenges and threats to humanity and the environment that we once perceived to be safe and secure. These adverse climate changes will impact all aspects of human, natural life, and environmental services. Researchers engaged in impact studies of climate change have summarized these impacts as follows:

• Climate change-induced warmer temperatures have escalated the frequency, intensity, and duration of heat waves, posing health risks, especially for young children and the elderly (Vose et al., 2017).

• Climate change has deleterious implications for human health by worsening air and water quality, facilitating the spread of certain diseases, and altering the frequency or intensity of extreme weather events (Fann et al., 2016).

• Rising sea levels induced by climate change pose threats to human communities and ecosystems in coastal regions worldwide (Fleming et al., 2018).

• Changes in rainfall patterns and streamflow timing and amount, resulting from climate change, impact water supply and quality and hydroelectricity production in many parts of the world (Lall et al., 2018).

• Changes in ecosystems induced by climate change have influenced the geo- graphic ranges of numerous plant and animal species and the timing of their life cycle events, such as migration and reproduction (Lipton et al., 2018).

• The increased frequency and intensity of extreme weather events due to climate change, such as heat waves, droughts, and floods, lead to property losses, societal disruptions, and decreased insurance affordability (Ebi et al., 2018).