Climate change is an issue that’s been kicked around like a political football in Australia for many years, but local scientists have already undertaken the research and modelling to work out what the adverse impacts will be in the Wet Tropics, including how water, waterways and coastal systems will be affected.

In terms of the big picture, we know with a fair degree of confidence that rainfall patterns will be less predictable and there will be more extreme weather events like cyclones, land and marine heatwaves and heavy rainfalls.

Some of the key impacts that could affect our waterways include:

1. Sea level rise

Rising sea levels are being caused by a combination of ice sheets and glaciers melting and thermal expansion of seawater as it heats up. Since 1880 global mean sea level has risen by about 25cm with about half of this happening since 1970. By the end of this century, it is estimated that the global mean sea level rise will be at least 50 cm, even if we drastically reduce greenhouse gas emissions. Under high emission scenarios it could be up to one metre by 2100.

The most significant impact of this will be to our coastal communities. Some low-lying areas will become permanently submerged while others will only be inundated during high tide or storm tides associated with cyclones. Saltwater intrusion will affect wetlands, mangroves, seagrass beds, reefs, lakes and dams. Even groundwater will be affected in some areas so farming will be adversely impacted.

2. More extreme weather events

Cyclones are a feature of our tropical climate and modelling predicts that they are likely to become less frequent but more intense with climate change. When combined with rising sea levels, this will mean more intense and frequent storm surges and coastal flooding. This has implications for coastal settlements, but it will also cause damage to natural barriers like sand dunes and mangroves which buffer the land and keep the ocean and freshwater habitats separate.

3. Warmer water temperatures

Marine heatwaves, caused by increasing sea surface temperatures, are already the biggest threat to the Great Barrier Reef. In the last five years there have been three mass coral bleaching events. This is a natural phenomenon, but climate change is causing them to happen much more frequently, which means that coral reefs won’t have time to recover between each event.

Lots of other important biological processes are regulated by temperature, including the reproduction of animals like turtles and crocodiles. The gender of these animals is determined by the temperature of their nests, with warmer temperatures producing more females than males, which has implications for their future populations.

Our rivers and waterways will also be affected by a decreasing ability of water to hold dissolved oxygen as temperatures rise. Dissolved oxygen is critical for life in waterways and sensitive species, such as larger fish, are particularly vulnerable to declines in dissolved oxygen. For example, these conditions in the ocean will favour more jellyfish rather than big fast swimming species like tuna. Over the last few decades there have been marked decreases in dissolved oxygen and this trend is projected to continue.

Water temperature is also a critical cue for behaviour of fish species during the year. Seasonal changes of temperature in waterways affect the onset of fish movements and reproductive patterns. As water temperatures rise and fall out of season, the movement and behavioral patterns of fish are disrupted and reproduction is inhibited.

What can we do to mitigate these impacts?

While the world is (hopefully) moving swiftly towards reducing greenhouse gas emissions, we can help build the resilience of our region to adapt to the changing climate conditions through:

• Restoration of mangroves, riparian vegetation, littoral rainforest and beach and dune vegetation to provide coastal protection against cyclones, storm surges, erosion and salinity.
• Planting salt resistant vegetation further inland.
• Restoring coral reefs and coastal dune systems.
• Helping mangroves to establish further inland.
• Improving water use efficiency and recycling.

More information

For more information about the implications of climate change for the Wet Tropics, go to the Wet Tropics Plan for People & Country.