In its forthcoming issue, National Review ridicules unnamed offenders who have purportedly distorted science to blame manmade climate change for both drought and flooding in Australia:

Weather extremes used to be taken for granted Down Under, but in recent years, each new drought has been attributed to (can you guess?) global warming. Unless greenhouse gases were sharply reduced, it was predicted, Australia would never again have enough water. Now the lucky country is experiencing violent, destructive floods, and the Australian intelligentsia has fingered the exact same versatile phenomenon as the culprit. Is there anything global warming can't do? We half expect Charlie Sheen and the NFL lockout to be linked to it. [National Review, 4/4/11, via Nexis]

National Review does a good job here of showing how much easier it is to create confusion than to inform on the issue of climate change. By mocking the notion that global warming could intensify both drought and flooding, National Review perpetuates misunderstanding of climate science and the false perception that scientists are clueless and/or dishonest.

It's simply not true that the climate science community has recently changed its tune from warning about drought in Australia to warning about flooding. Back in 2001, the Intergovernmental Panel on Climate Change projected "[i]ncreased frequency of high-intensity rainfall, which is likely to increase flood damage" for Australia and New Zealand as well as "[r]egional reductions in rainfall in south-west and inland Australia and eastern New Zealand."

It should also be noted that National Review does not identify a climate scientist or scientific body, but rather criticizes a vague “Australian intelligentsia” for blaming climate change for both drought and recent floods. This may be because climate scientists are actually quite careful not to blame anthropogenic global warming for individual weather events since natural variation is a larger factor on shorter time scales than longer-term timescales. At the same time, as Australian science blogger John Cook explains, “it's equally false to say global warming has no effect on weather”:

An apt metaphor to understand how weather works is to consider the rolling of dice, which can be just as chaotic and unpredictable. What if you load the dice so one face is heavier? This increases the chances of rolling a certain number. Global warming loads the dice, and here's how.

As the climate gets warmer, more water evaporates and the air holds more moisture. Over the past 40 years, the amount of water vapour in the atmosphere has risen by 4%. Lately in Australia, we've been measuring everything by Sydney Harbours. Globally, the amount of extra water vapour in the air due to warming is equivalent to more than 900 Sydney Harbours. All that extra water vapour increases the chance of an extreme rainfall event.

It's not appropriate to say global warming causes a particular weather event. But it's equally false to say global warming has no effect on weather. Yes, we've had floods and heavy downpours in the past, well before modern global warming. But now the odds of heavy downpours and floods are increasing.

In fact, our physical understanding of climate tells us global warming will cause the water cycle to grow more intense. This means both more heavy downpours and more intense drought. As temperatures rise, the ground dries out faster, causing droughts to get worse. So we find ourselves swinging from one extreme to another, like an ever deepening rollercoaster ride.

Karl Braganza of Australia's Bureau of Meteorology has said that while the relative contribution of global warming to particular instances of extreme weather has been difficult for scientists to quantify, ''The physics of the climate system means that variability at all timescales is influenced by global warming." From The Age:

Increasing levels of greenhouse gases, particularly carbon dioxide emitted by burning fossil fuels, affects all our weather to some degree, scientists say.

Aspects of recent extreme-weather events seem to be the result of global warming and natural climate variability pushing in the same direction, says Karl Braganza, the manager of climate monitoring at the Bureau of Meteorology's National Climate Centre in Melbourne.

Climate scientists, he explains, talk of climate variability on a range of timescales: from day-to-day weather to seasonal and year-to-year variability -- and beyond to climate variability and climate change.

''The physics of the climate system means that variability at all timescales is influenced by global warming,'' he says.

How so? The effect of increasing greenhouse gases, Dr Braganza says, is overlaid on naturally occurring climate variability, which is governed by the physics of the Earth's atmosphere. ''The two mechanisms operate in conjunction.''

Similarly, the Sydney Morning Herald reported on January 12 that David Karoly of the School of Earth Sciences at the University of Melbourne “stressed individual events could not be attributed to climate change. But the wild extremes being experienced by the continent were in keeping with scientists' forecasts of more flooding associated with increased heavy rain and more droughts as a result of high temperatures and more evaporation”:

THE strong La Nina pattern taking moisture to north-eastern Australia has been exaggerated by record high ocean temperatures, a combination not seen on this scale since the deadly Brisbane flood of 1974 which claimed at least 14 lives.

And while Queensland's already saturated catchments are lashed with heavy rain, south-western Western Australia is experiencing an extreme dry - and bushfires.

''Australia has been known for more than 100 years as a land of droughts and flooding rains, but what climate change means is Australia becomes a land of more droughts and worse flooding rains,'' David Karoly, from Melbourne University's school of earth sciences, said.

Professor Karoly stressed individual events could not be attributed to climate change. But the wild extremes being experienced by the continent were in keeping with scientists' forecasts of more flooding associated with increased heavy rain and more droughts as a result of high temperatures and more evaporation.

''On some measures it's the strongest La Nina in recorded history ... [but] we also have record-high ocean temperatures in northern Australia which means more moisture evaporating into the air,'' he said. ''And that means lots of heavy rain.''

Karoly further stated via email that “climate change is expected to lead to both more droughts in Australia and more flooding, just not in the same place at the same time”:

Australia has a highly variable climate, affected by large swings in ocean temperatures in the equatorial Pacific Ocean from El Nino to La Nina phases.

These contribute to increased risk of drought during El Nino and increased risk of heavy rain in La Nina events. We are currently in a very strong La Nina event, which is the main reason for the heavy rainfall and flooding in eastern Australia.

In addition to the La Nina, we also have a long-term warming trend in ocean temperatures around Australia, with record high ocean temps around Australia over the last 6 months. This increase in ocean temperatures is part of global warming due to increasing greenhouse gases.

The warmer ocean temperatures cause more moisture in the atmosphere and contribute to heavier rainfall and flooding.

Projections of climate change impacts in Australia include more hot extremes and heat waves, reduced rainfall and worse droughts in southern Australia, as well as more heavy precipitation and flooding events, as the warmer atmosphere can hold more water.

So climate change is expected to lead to both more droughts in Australia and more flooding, just not in the same place at the same time.