(CNN) The final figures are in for air passenger traffic in 2019 at the world's busiest airports.

The 2019 list of the world's busiest airports, released by ACI on Thursday, showed a 3.5% increase in passenger numbers -- coming in at more than 9.1 billion -- compared with 2018.

For the first time, the report looks ahead at the drastic declines that came in the first half of 2020 as Covid-19 outbreaks decimated passenger traffic.

Passenger numbers decreased by 58.4% worldwide in the first half of 2020, compared with the same period in 2019, with international passenger traffic hit the hardest, with a 64.5% drop.

Atlanta and Beijing airports held the top two spots in 2019, with more than 110 million and 100 million passengers, respectively. But those airports saw passenger traffic drops of 56.6% and 73.6% in the first half of 2020.

Los Angeles International Airport moved up one spot in 2019 to become the third busiest airport for passenger traffic, with more than 88 million passengers in 2019. Passenger traffic there dropped 58.9% in the first half of 2020.

Path to recovery

The airport industry is anticipating a 60% reduction in revenues compared to previous projections, according to ACI.

The organization and its industry partners see reducing travel restrictions and quarantine requirements and a global approach to testing for the virus as keys to recovery.

"We are positive about the future, but we need consistency and collaboration across the globe on key issues like testing," said ACI World Director General Luis Felipe de Oliveira, in a statement.

"The industry is united in the view that widespread testing of passengers before travel, as an alternative to quarantine restrictions, will be a crucial way to foster public confidence in air travel and must be introduced."

ACI is aligning itself with the International Civil Aviation Organization (ICAO) and the World Health Organization (WHO) in its call for efficient, standardized testing, but ultimately countries would be responsible for working out a coordinated approach.

Testing as a safety measure that would boost traveler confidence is just one measure needed, not just for aviation's recovery, but for all the industries that are interconnected, says Patrick Lucas, ACI World's head of airport business analytics.

"When airports and airlines ask for these things, it's not just for our industry per se, it's because we're so connected to other industries. We're very much connected to, of course, tourism and the hospitality industries."

About 60% of tourists arrive by air, Lucas said, "so everything that is connected to the tourists -- the restaurants and so on and so forth, all those businesses are connected."

Air travel has started to tick up from the darkest days in April, when traffic declines of more than 90% were recorded, but a full recovery is likely several years away.

World's top 10 busiest airports

1. Atlanta (ATL) -- 110.5 million passengers in 2019; traffic dropped 56.6% in the first half of 2020

2. Beijing (PEK) -- 100 million passengers in 2019; traffic dropped 73.6% in the first half of 2020

3. Los Angeles (LAX) -- 88.1 million passengers in 2019; traffic dropped 58.9% in the first half of 2020

4. Dubai (DXB) -- 86.4 million passengers in 2019; traffic dropped by 56.4% in the first half of 2020

5. Tokyo (HND) -- 85.5 million passengers in 2019; traffic dropped by 59.2% in the first half of 2020

6. Chicago (ORD) -- 84.6 million passengers in 2019; traffic dropped by 57.6% in the first half of 2020

7. London (LHR) -- 80.9 million passengers in 2019; traffic dropped by 60.2% in the first half of 2020

8. Shanghai (PVG) -- 76.2 million passengers in 2019; traffic dropped by 68.1% in the first half of 2020

9. Paris (CDG) -- 76.2 million passengers in 2019; traffic dropped by 61.4% in the first half of 2020

10. Dallas/Fort Worth (DFW) -- 75.1 million passengers in 2019; traffic dropped by 48.2% in the first half of 2020

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The world's busiest airports -- and how far they've fallen - CNN