Australian Open extreme heat policy
The Australian Open Extreme Heat Policy (EHP) will be applied at the Referee's discretion and may be altered at any time.
At the Referee's discretion, when the Wet Bulb Globe Temperature only (WBGT) is equal to or above the pre-determined threshold, the Referee may suspend the commencement of any further matches on outside courts.
Any matches currently in progress will continue until the end of the current set. At the completion of the set, play will be suspended.
Where play in any match commences outdoors (or with a roof open) and the WBGT temperature is equal to or exceeds the pre-determined threshold, the match will continue until the completion of the set. At the end of the set a decision may be made by the Referee to close the roof for the remainder of the match and the following matches, when the EHP is still in effect.
A roof will only be closed because of extreme heat if a decision has been made by the Referee to suspend the completion or commencement of matches on the outdoor courts.
Supplement for women’s singles and junior singles only; to allow a 10-minute break between the second and third sets when a WBGT reading of 28 has been recorded prior to the calling of the match by Tournament Control. Readings are continually made throughout the day.
The 10-minute break will not apply between the second and third sets, if play had previously been suspended after the first set due to the EHP.
The WBGT is used to help decide whether the EHP should be implemented. The WBGT is a measure of heat stress index and takes into account the actual temperature as well as radiation, wind, and humidity. It is a combination of the WBGT with the actual air temperature that is used to decide whether the EHP is activated.
The Australian Open temperature threshold has now been increased to 40°C (104°F). The WBGT threshold has now been increased to 32.5. In rare instances where both of these high thresholds are met, additional factors are taken into account by the tournament referee, including the forecast. 
Changes for 2015 Australian Open
Following severe criticism of the handling of the 2014 Australian Open, organizers increased the temperature threshold from the 2003 level of 35°C (95°F) to 40°C (104°F) and increased the WBGT threshold from the 2003 level of 28 to 32.5 to allow for more continuous play and less stoppages in the future. 
'The heat policy, as always, will be applied at the Referee's discretion,' said Tennis Australia CEO Craig Tiley. 'The decision on implementing the heat policy will take into account the forecast once the ambient temperature exceeds 40 degrees Celsius, and the Wet Bulb Global Temperature (WBGT) reading exceeds 32.5,' he said. 'When conditions exceed these levels the Referee is taking into account the forecast and state of play when making his discretionary call.'
WBGT charts show that the new threshold may not be triggered even if the temperature reaches 50°C (122°F) when there is no humidity. 
When the policy is implemented, matches will now be halted after an even number of games in the set, rather than at the conclusion of the set.
There will also be a retractable roof available on Margaret Court Arena for the first time.
In 1988, Rod Laver Arena opened making the Australian Open the first Grand Slam to feature a retractable roof. The initial heat policy allowed for the roof to be closed when the temperature rose above 39°C (102°F) or at the referee's discretion when the temperature rose above 35°C (95°F), but only for daytime matches and only once all singles matches could be scheduled inside Rod Laver Arena. This effectively meant that the heat policy could only go in effect in the quarterfinals or later in the tournament.
The heat rule was first invoked during the quarterfinal round in 1997.
In 1998 a new policy was implemented calling for play on all courts to be stopped if the temperature reached 40°C (104°F). This was later changed in 2002 to 38°C (100°F).
The 2002 women's final was played in 35°C (95°F) heat, which triggered a 10 minute break between the 2nd and 3rd sets but no halt in play.
Beginning with the 2003 tournament the policy was changed to 35°C (95°F) and a WBGT of 28. 
The new policy was invoked on January 20, 2003 on a day when the temperature reached 37°C (98.6°F) and the WBGT reached the 28 mark.  Play was halted for the minimum 2 hours.
After the extreme heat policy was invoked in consecutive years in 2006 and 2007, the policy was again changed starting in 2008 to allow matches in progress to be halted at the conclusion of the set. Prior to that a match already underway had to be completed. The policy was further changed in 2008 to allow play to be stopped only at the discretion of the tournament referee, rather than relying solely on temperature and WBGT calculations.
The policy was invoked several times in 2009, the hottest tournament to date with an average temperature of 34.7°C (94.5°F). 
2014 Australian Open
The extreme heat policy came under criticism during the 2014 Australian Open after ballboys, attendants in the stands, and players were suffering various heat-related illnesses due to 4 consecutive brutal days with highs between 41.5°C (106.7°F) and 43.9°C (111°F), but organizers claimed the humidity remained low enough on all but one day for the policy not to be enforced; tournament referee Wayne McKewen said that "While conditions were hot and uncomfortable, the relatively low level of humidity ensured that conditions never deteriorated to a point where it was necessary to invoke the extreme heat policy". Frank Dancevic, who began to hallucinate and collapse during his 6–7(12–14), 3–6, 4–6 loss to Benoît Paire, described the conditions as "inhumane" while severely criticising the policy, and Andy Murray voiced his concerns about people's safety, stating that "it only takes one bad thing to happen". Ivan Dodig, who also collapsed and was forced to retire, said afterwards that he was "thinking he could maybe even die" in the extreme conditions. Nine players retired during the second day, while Daniel Gimeno-Traver carried off a ball boy who fainted during his match and Peng Shuai was amongst many throughout the tournament that required medical attention. Jo-Wilfried Tsonga and Caroline Wozniacki noted that their shoes and water bottles were beginning to melt in the conditions, while Serena Williams and Victoria Azarenka said that the heat was affecting their play.
Roger Federer, however, agreed with the referee's decision, saying that adequate training and preparation should be enough to cope with the weather. Gilles Simon, who was injured prior to the tournament, took a similar view and said that the heat improved his game.
On the second day of the tournament the temperature reached 42.2°C. On the third day it reached 41.5°C. On the fourth day it reached 43.3°C. On the fifth day it reached 43.9°C with 6% humidity. Play continued uninterrupted for the second, third, and fifth days and was stopped for 4 hours on the fourth day.  For many players the stoppage was closer to 3 hours because they had to complete the set in progress even after the policy went into effect. On Rod Laver Arena, Maria Sharapova and Karin Knapp had to complete a 3rd set that lasted nearly 2 hours and 18 games. On the third day 970 fans had been treated for heat exhaustion. 
While the exact WGBT on these days has not been revealed by the organizers, it is clear that had the earlier 1998 policy been still in effect play would have been halted all 4 days once the temperature exceeded 40 degrees Celsius
The extreme heat resulted in a record number of 9 withdraws in the first round.
On January 24, 2015, the Herald Sun reported that Susan Carman sued the Melbourne & Olympic Parks Trust for failing to close the roof at Hisense Arena during Andy Murray's second round match in the 2013 Australian Open. The temperature that day reached 40°C (104°F). Carman says she fell down the stairs while seeking shade. 
- "Australian Open - Tournament Facts". The Australian Open Tennis Tournament. Retrieved 17 January 2013.
- "Australian Open slammed for 'inhumane' conditions in extreme heat". Guardian. 15 January 2014. Retrieved 15 January 2014.
- "As players and ballboys collapse in 42C Australian heat, Murray sticks up for stricken stars who blast... it's so cruel!". Daily Mail. 15 January 2014. Retrieved 15 January 2014.
- "Australian Open 2014: Ivan Dodig thought he may 'die' after collapsing due to brutal heat". Daily Star. 15 January 2014. Retrieved 16 January 2014.
- "Players, officials affected by Australian Open heat". Burlington Free Press. 14 January 2014. Retrieved 16 January 2014.