The phrase "also warn that it" is correct and usable in written English.
You can use it when indicating that there is an additional caution or alert regarding a specific subject or situation.
Example: "The researchers also warn that it may take longer than expected to see results from the new treatment."
Alternatives: "also caution that it" or "also alert that it".
They should also warn that it has a deficient understanding of human life; part of this is its implied belief in natural human goodness.
Experts also warn that it is early yet in the natural history of West Nile in North America, so it is hard to know what the numbers mean, and it is harder still to make any predictions.
Although you wisely note that the zeal for scoops may lead to inaccuracy, you should also warn that it leads reporters to court leakers and ignore the leakers' often tawdry motives and dubious accuracy in gratitude for the scoop.
Critics of the legislation also warn that it will hurt some lower-income workers in small businesses by discouraging their employers from offering plans and by encouraging some others to cut future benefits.
But Harman, who has been at the forefront of Britain's feminist movement for decades, will also warn that it is "raining men" at the top of the Labour party, which is embarrassing while the Tory party, the SNP, Greens and even Ukip have female leaders.
But they also warn that it is more important to monitor individual tiger populations every year to really get a handle on their health.
He also warned that "it is possible we will discover further British nationals once the building is fully secured".
He also warned that "it may not be pretty".
In its second profits warning in just two months, Savills also warned that it is reviewing its dividend policy.
Wachovia also warned that it would increase its provision for future loan losses by $200 million.
RIM also warned that it would report its first quarterly operating loss for eight years in the current quarter.
