Evidence of climate change first became apparent in the more sensitive ecosystems around the world. These systems have since then been used in research to highlight how the climate has developed historically, what the current situation is, and what is likely to happen in the near and distant future.

For decades, signals of warming have been recorded in high alpine areas. Glaciers are melting at an accelerating pace (Haeberli and Beniston 1998) and current research predicts that most glaciers in the European Alps will be gone by the year 2100 (Zekollari et al. 2019). The effects of climate change are also evident in coral reefs around the world, where rising sea surface temperatures cause increasingly frequent and damaging bleaching events (Goreau and Hayes 1994). At the regional scale, the pace of warming is faster in the polar regions than the global average. This has now led to profound shifts in the distribution of plant and animal species—terrestrial as well as aquatic (IPCC 2013).

Although climate change is evident, determining the effects it has is in itself difficult as it is entangled with other large-scale environmental changes. For example, high CO2 concentrations lead also to ocean acidification. This creates what is often referred to as “the other CO2 problem” (Caldeira and Wickett 2003)—a lower buffering capacity. Together, increasing temperature and acidification result in accelerating cascade effects in marine ecosystems and may cause sudden shifts in the structure and function of ecosystems. Such dramatic shifts are visible in most coral reefs as they are pushed closer to the final tipping point where the reefs are beyond recovery (Hoegh-Guldberg et al. 2007; Smith et al. 2020; Goreau and Hayes 2021). Scientists studying such systems were among the first to raise alarm and warn about the consequences of global warming for diverse ecosystems and the people inhabiting or depending on them for their livelihoods.

The number of publications concerning “climate change” in the database Web of Science “Environmental Sciences” and “Meteorology Atmospheric Sciences”, has increased from less than 10 publications per year between 1945 and 1985, to well over 1000 from 2003, peaking with over 10 000 per year after 2017.Footnote 1 Climate change has also received more attention in Ambio, with on average 32 publications per year during the previous decade.

In this anniversary collection, we present four highly cited Ambio papers that were important for the early discovery and understanding of climate change effects in three types of ecosystems; coral reefs (Goreau and Hayes 1994), European Alps (Haeberli and Beniston 1998), and the terrestrial Arctic (Callaghan et al. 2004, 2011). The authors of these four papers offer their personal views and behind the paper stories (Callaghan and Johansson 2021; Goreau and Hayes 2021; Haeberli and Beniston 2021). In addition, three other scientists reflect on the four papers and put them in perspective (Chen 2021; Bjorkman and Wulff 2021). Taken together, these papers provide evidence of the escalating effects of climate change on vulnerable ecosystems worldwide—and the signals we receive are deep red.

The Ambio papers highlighted in this anniversary collection also argue for improving the monitoring of abiotic as well as biotic facets of climate change impacts (see below). A number of such initiatives to monitor climate change are now in place: the Circumpolar Biodiversity Monitoring Program (CBMPFootnote 2), developed by the Conservation of Arctic Flora and Fauna working group of the Arctic Council (marine, freshwater, terrestrial, and coastal ecosystems in the Arctic), the Global Mountain Biodiversity Assessment (GMBAFootnote 3), and the Global Coral Reef Monitoring Network (GCRMNFootnote 4). The results from these and other research efforts are used by the Intergovernmental Panel on Climate Change (IPCC) to regularly publish state-of-the-art climate change updates, such as the recent special report on the ocean and cryosphere in a changing climate (IPCC 2019). This report presented the most recent assessments of climate-related risks for oceans, polar and high mountain regions. For coral reefs, a further loss of 70–90% at 1.5 °C global warming is anticipated, Arctic sea ice will continue to melt, and small glaciers (e.g. in the European Alps) are projected to disappear by 2100 (IPCC 2019). The occurrence of multifactorial effects makes scientists less certain about how ecosystems will respond to these changes. For example, ocean acidification and reduced oxygen levels pose additive threats to coral reefs. Moreover, some locations in e.g. Arctic ecosystems, for reasons not yet clear, seem resistant to climate change (so far) (Taylor et al. 2020); something that needs to be further explored to gain knowledge on how to mitigate ongoing (negative) changes.

Climate change represents one of the most pressing societal and scientific challenges of our time. The four influential papers (Goreau and Hayes 1994; Haeberli and Beniston 1998; Callaghan et al. 2004, 2011) established baseline facts and helped raise awareness. There is now a broad consensus that trends of climate warming over the past century are caused by human activities, like the burning of fossil fuels (Oreskes 2004; Cook et al. 2016), and the majority of the world’s leading scientific organisations have issued public statements endorsing this position. Young people around the world are making a strong call for action and so are the people living in the regions most affected by climate change effects. In the Paris Agreement 2015, the World leaders agreed to limit global warming, but these ambitions have not been fulfilled.

On the positive side, history demonstrates that we can act together and make changes for the common good. One such example is the Montreal Protocol on substances that deplete the ozone layer, adopted 1987, and today, the parties have phased out ca. 98% of ozone-depleting substances. Another example is the progress in reduction of emissions of acidifying sulfur and nitrogen oxides, which together with liming has led to gradual recovery of the chemistry and biology of inland waters (see Tranvik 2021).

If we want to, we can make changes.

figure a
figure b
figure c
figure d