All organisms modify their environment, and so do humans. As the human population has grown and the power of technology has expanded, the intensity and nature of this alteration has drastically increased. Most of all ecosystems are dominated by humans, and no ecosystem on Earth’s surface is free of prevalent human influence (Vitousek et al., 1997). This is an Epoch called Anthropocene (Lewis & Maslin, 2015), where species extinction is happening at unprecedented rates (1,000 times faster than it should without human activities). Thus, humanity is responsible for the sixth mass extinction, the only one caused by a living organism. Four major anthropogenic activities are key drivers of this biodiversity loss; (i) habitat loss and fragmentation, (ii) global climate change (iii) invasive alien species and (iv) natural resource overexploitation (e.g. over-hunting, over-fishing). As my previous article on these pages talked about the effects of habitat loss and fragmentation on biodiversity, the present article will discuss how climate change, mainly global warming, can affect biodiversity (and human well-being) by (i) displacing species pole-wards or further up in elevation, (ii) changing species interactions, and leading to (iii) biodiversity loss (species extinction). Since 40% of world’s economy is derived from biological resources (Reed, 2012), biodiversity loss will drastically lower the quality of human life and will take millions of years to reverse. If humanity is to survive this ecocide, we need to halt human over-population and natural capital over-consumption. The climate (long-term weather patterns of a region, including temperature, wind, humidity, and precipitation) of the Earth is affected by two competing processes: greenhouse gas effect and atmospheric convection (Spencer, 2009). Solar energy is converted to heat when it reaches the Earth. Almost 40% of that heat is reflected into space. This is known as Earth’s albedo or reflectivity. Due to gases called greenhouse gases (CO2, water vapors, methane, nitrogen oxides, chlorofluorocarbon, hydrofluorocarbon, sulfur hexafluoride, and nitrogen trifluoride) that heat does not continue upper in the atmosphere, which acts to warm the lower atmosphere. This process is known as global warming. Major greenhouse gas emissions are from the burning of fossil fuels (coal, oil, and natural gas), deforestation, and intensive livestock farming (Ripple et al., 2014), and the main greenhouse gas is CO2. Climate models forecast that atmospheric CO2 concentrations will be 1, 000 parts per million (ppm), from current concentrations of 480 ppm. As a result, global air temperature will rise by 4.8 0C by the end of this century (IPCC, 2013). This increase in global air temperature will have strong impacts on biological communities and ecological processes (Friberg et al., 2009). For instance, 20-30% of animal and plants species are likely to be at increased risk of extinction if increases in global temperature exceed 1.5 to 2.5 0C (IPCC, 2007). For millions of years, species have evolved to survive within certain temperature ranges, and temperature decreases with increasing altitude and latitude. So, when temperature increases, some species are expected to retreat pole-wards or to higher altitudes (Parmesan, 2006). Unfortunately, natural landscapes have been severely fragmented that some species will have no ways to track their environmental conditions. Mountain gorillas, say, are in the roof of Rwanda, they occupy the highest ecosystem (Volcanoes National Park) above sea-level in Rwanda. They have no further up to go, in this country. They should escape to the Swiss Alps, but, of course, that will be nearly boiling the ocean. Cairo and Madrid will be in their way, they will be caught between a rock and a hard place. They will either adapt or they will go extinct, but, since nature abhors a vacuum, other species may flourish to occupy the vacant ecological niche. For the latter, climate warming will not be just an ill wind that blows no good. As a way of adaptation, other species will modify their life histories and phenology (Root et al., 2003), metabolic rates and body size (Brown et al., 2004). According to the thermal reaction norm, ectotherms (cold-blooded animals) reared at high temperature lay small eggs and have a small size as adults, which has a negative effect on their fitness (survival, fecundity, and mating success) (Honek, 1993). These changes will negatively impact species interactions (Hughes, 2000), where many species will be doomed to extinction. Moreover, there are species with temperature – and genotypic-dependent sex determination, TSD and GSD, respectively. Some species exhibiting TSD produce males only at low temperatures (Hays et al., 2017). For these species, there is fear that increasing temperature will lead to single-sex populations and, therefore, population or species extinction. Rising temperatures will lead to the melting of glaciers, rising sea level, coral bleaching (Plass-Johnson et al., 2015), frequent wildfires, and desertification of already arid regions. It is also expected that, due to climate change, the Earth will face heavy rainfalls (since evaporation increases with temperature) which will increase erosion and nutrients loading in aquatic ecosystems (Rosenzweig et al, 2007). This high nutrient concentration in water bodies will result in eutrophic (high concentration of nutrients) and anoxic (deprived of oxygen) systems known as dead zones (Broman et al., 2017). On the other hand, elevated CO2 will result in wood encroachment in savannahs (Stevens et al., 2016), ocean acidification (Wood et al., 2016), plants/crops with less nutritional value for humans and other living organisms (Dietterich et al., 2015), and, of course, global warming. Environmental problems have been the root cause of numerous collapses, including Rapa Nui, Maya, and Norse civilizations, in the past (Diamond, 2005). These were just local or regional collapses. But today, humanity’s global civilization, the worldwide, increasingly interconnected, highly technological society in which we all are, to one degree or another, embedded, is threatened with collapse. Anthropogenic activities, transportation means and food production, are the main cause of climate change. Climate change is causing species extinction, and ecosystem services (benefits humans obtain from ecosystems) from these species are critical to human well-being. Thus, losing natural ecosystems will lower the quality of our life. To paraphrase Jared Diamond (in his “The rise and the fall of the third chimpanzee, 1991”), I would not have written this article if I thought that the threat was remote, but I also would not have written it if I considered our situation hopeless. The Paris agreement reached at the COP21 in 2015 was a historic milestone and represented an international compromise to hold the increase of global average temperature to well below 2 0C above pre-industrial levels and pursue efforts to limit the temperature increase to 1.5 0C above pre-industrial levels (UNFCCC, 2015). The agreement makes it clear that scientists are not trying to make a mountain out of a molehill when they talk about climate change. Additionally, the agreement understands that science has made it clear that there is no time to let the dust settle. And science has done a lot (even though being far from enough) to light a fire under global leaders who signed the Paris agreement, on December 12, 2015. The Paris report of the UNFCCC clearly outlines what should be done to mitigate and adapt to climate change, but people can also have a look at the latest “World scientists’ warning of a climate emergency, 2019”. The writer is a PhD student in Ecology and Environmental sciences at the University of Barcelona. His doctoral thesis is about the Impact of dam decommissioning on two greenhouse gases, methane (CH4) and carbon dioxide (CO2). The views expressed in this article are of the author.
