Summary
People flocked to the beach for respite one evening during Melbourne’s record breaking four-day heatwave in January 2014, under a sky made hazy by smoke from a scrub fire.
by
Neil O’Connor
Earth’s climate has changed over the past century. The atmosphere and oceans have warmed, sea levels have risen, and glaciers and ice sheets have decreased in size. The best available evidence indicates that greenhouse gas emissions from human activities are the main cause. Continuing increases in greenhouse gases will produce further warming and other changes in Earth’s physical environment and ecosystems.
The science behind these statements is supported by extensive studies based on four main lines of evidence:
- Physical principles established more than a century ago tell us that certain trace gases in the atmosphere, such as carbon dioxide (CO2) and water vapour, restrict the radiant flow of heat from Earth to space. This mechanism, known as the ‘greenhouse effect’, keeps Earth’s surface and lower atmosphere considerably warmer than they would otherwise be. The gases involved are called ‘greenhouse gases’. An increase in greenhouse gas concentrations raises the temperature of the surface.
- The record of the distant past(millions of years) tells us that climate has varied greatly through Earth’s history. It has, for example, gone through ten major ice age cycles over approximately the past million years. Over the last few thousand years of this period, during which civilisations developed, climate was unusually stable. Evidence from the past confirms that climate can be sensitive to small persistent changes, such as variations in Earth’s orbit.
- Measurements from the recent past (the last 150 years) tell us that Earth’s surface has warmed as atmospheric concentrations of greenhouse gases increased through human activities, and that this warming has led to other environmental changes. Although climate varies from decade to decade, the overall upward trend of average global surface temperature over the last century is clear.
- Climate models allow us to understand the causes of past climate changes, and to project climate change into the future. Together with physical principles and knowledge of past variations, models provide compelling evidence that recent changes are due to increased greenhouse gas concentrations in the atmosphere. They tell us that, unless greenhouse gas emissions are reduced greatly and greenhouse gas concentrations are stabilised, greenhouse warming will continue to increase.
This document aims to summarise and clarify the current scientific understanding of climate change by answering nine key questions.
Summary | Australian Academy of Science
Now that is what the Australian Academy of Science says, not three non-entities. Far from being laughed at, most Australian scientists state the global warming is real.
Does kinda make the alarmist contingent look silly.
