Exceptions to this drop in growth rate occurred in 1991 and 1998 when growth rates increased suddenly to 14-15 nmol/mol per year for those years, nearly double the growth rates of the years before.
As únicas excepcións a esta diminución ocorreron entre 1991 e 1998 cando as taxas de aumento se incrementaron repentinamente a 14-15 nmol/mol por ano, case o dobre que as dos anos anteriores.