evidence: The State of the Climate report showed that the average pH of surface waters around Australia has decreased by about 0.12 between the periods 1880–1889 and 2010–2019. Being a logarithmic scale, a decrease in the pH of one unit translates to a 10-fold increase in acidity. Therefore, acidity of surface waters around Australia has increased more than 30 per cent over the past 140 years. The cause of this drop in pH is rising carbon dioxide levels in the atmosphere. When carbon dioxide levels in the atmosphere are higher than those of ocean surface waters, the water absorbs carbon dioxide. At high latitudes, these carbon dioxide-laden surface waters become cold and salty enough to sink to the deep sea. Deeper water is then pushed up to replace the sinking surface water. This new surface water absorbs more carbon dioxide and so the cycle starts again. It is this connection between surface and deep waters in seas at higher latitudes that is the main pathway enabling uptake of carbon dioxide emissions by our oceans. [...] The State of the Climate report is clear on what the future holds for Australia’s climate. The amount of climate change expected in the next decade is similar under all plausible global emissions scenarios. However, by the mid-21st century, higher ongoing emissions of greenhouse gases will lead to greater ocean acidification and warming - with all their associated impacts. Reducing emissions will lead to less ocean acidification and warming, and fewer impacts.